Do you drink water that's been left sitting out overnight or even for another day? Have you noticed it tastes different?

    Tap water that has been left to sit out slowly begins to acquire(获得) off taste. Many people think that this is because of microorganisms. But that's not what makes old water taste not fresh. For that we can thank carbon dioxide. After about 12 hours, tap water starts to go flat as carbon dioxide in the air starts to mix with the water in the glass, lowering its pH and giving it an off taste. But it's most likely safe to drink.

    However, back to those microorganisms. If you use a dirty glass day after day, there is more of a chance of bacteria making themselves known; a risk that increases if you share the glass with another mouth as well. But assuming(假设) you use a fresh glass every few days, you probably won't have a problem unless the glass has been touched by dirty fingers, and especially if those dirty fingers went unwashed after using the bathroom.

    As for plastic water bottles that have been left out in the sun or in the car, step away from the bottle, warns Dr. Kellogg Schwab, director of the Johns Hopkins University Water Institute. "A chemical called biphenyl-A, or BPA, along with other things used to make plastic can leach(过滤) into your water if the bottle heats up or sits in the sun," he explains. BPA, as you probably know, has been linked to everything from heart disease to cancer. Schwab also adds that plastic used for commercial bottled water isn't meant to be washed or refilled, so use only one time and recycle. Or don't buy them at all; use refillable water bottles instead.

    "Hey, little boy, will you support me when I'm getting old?" Wang Wenshan, 35, asked his newborn baby as he hugged him at home.

    The Chinese tradition of raising sons to support parents in their old age has been weakened by the rapidly growing economy and improved standard of living. As is the case with more and more developed countries, China faces an aging society. People are living longer and having fewer children. Therefore, many Chinese families are falling into a 4-2-1 family pattern: a couple raises one child and supports four elderly parents. But few realize that a problem is likely to happen ahead.

    The aging of the population is a trend that now affects a growing number of countries. The Information Office of the State Council, China's cabinet, issued（发行） a white paper on measures China has been taking to help its elderly population. The paper said China's population entered the aging period at the end of the 20th century and the proportion of people aged 60 and above accounted for over 10 percent of the entire population. By the end of 2005, China had nearly 144 million people over 60, accounting for 11 percent of the population, according to the white paper.

An expanding aged population inevitably means that many issues must be settled, as the problem concerns every aspect of society. It puts more pressure on each family, causing disturbing economic consequences and serious social problems. It also challenges the labor force supply and the pension system.

    "I used to think that it's not an issue for me to provide for the aged," said Wang, whose parents and parents-in-law all enjoy pensions and medical insurance. But last year Wang's father suffered from a serious illness and afterward Wang began to feel the pressure on his shoulders.

    After his father recovered, Wang opened a bank account for each parent and put away some money in the account every month to prepare for future uncertainties. In addition, he has to save money every month to provide for his son's future education. "I'm now breaking my back to support my family: saving pensions for the parents, my son's education funds, and living costs."

    Wang also bought some commercial old-age insurance for himself. "We have to take precautions（预防） before it is too late, and many of my colleagues share the same view," he said.

    GOING TO UNIVERSITY is supposed to be a mind-broadening experience. That statement is probably made in comparison to training for work straight after school, which might not be so encouraging. But is it actually true? Jessika Golle of the University of Tübingen, in Germany, thought she would try to find out. Her result, however, is not quite what might be expected. As she reports in Psychological Science this week, she found that those who have been to university do indeed seem to leave with broader and more inquiring minds than those who have spent their immediate post-school years in vocational (职业的) training for work. However, it was not the case that university broadened minds. Rather, work seemed to narrow them.

    Dr. Golle came to this conclusion after she and a team of colleagues studied the early careers of 2,095 German youngsters. The team used two standardized tests to assess their volunteers. One was of personality traits, including openness, conscientiousness（认真）and so on. The other was of attitudes, such as realistic, investigative and enterprising. They administered both tests twice—once towards the end of each volunteer's time at school, and then again six years later. Of the original group, 382 were on the intermediate track, from which there was a choice between the academic and vocational routes, and it was on these that the researchers focused. University beckoned for 212 of them. The remaining 170 chose vocational training and a job.

    When it came to the second round of tests, Dr. Golle found that the personalities of those who had gone to university had not changed significantly. Those who had undergone vocational training and then got jobs were not that much changed in personality, either—except in one crucial respect. They had become more conscientious.

    That sounds like a good thing, certainly compared with the common public image of undergraduates as a bunch of lazybones. But changes in attitude that the researchers recorded were rather worrying. In the university group, again, none were detectable. But those who had chosen the vocational route showed marked drops in interest in tasks that are investigative and enterprising in nature. And that might restrict their choice of careers.

    Some investigative and enterprising jobs, such as scientific research, are, indeed beyond the degreeless. But many, particularly in Germany, with its tradition of vocational training, are not. The researchers mention, for example, computer programmers and finance-sector workers as careers requiring these traits. If Dr. Golle is correct, and changes in attitude brought about by the very training Germany prides itself on are narrowing people's choices, that is indeed a matter worthy of serious consideration.

Even though they're not the most exciting things in the world, plants have fascinated us ever since the days of early humans. They may not do any tricks or greet us when we come home at night like a dog would, but that doesn't mean they're any less interesting than animals.

However, just when we thought we knew everything we could about them, a recent study found that plants may possess a secret ability that's gone unnoticed all this time. According to the study by Australian biologist Monica Gagliano, published in the journal Oecologia, plants may be able to hear sounds.

To come to this conclusion, Gagliano and her team planted pea seedlings in a pair of different Y-shaped pots with two arms. The first pot's arms led to fresh water, while the other's led to either dry soil or a sealed plastic tube containing flowing water.

Naturally, the first pot's seedlings grew toward the water. What's surprising, however, is that the second pot's seedlings grew toward the sealed water supply and not the soil.

They just knew the water was there, even if the only thing to detect was the sound of it flowing inside the pipe, Gagliano told Scientific American. Gagliano believes that plants are able to use their leaves to detect sound waves, which make tiny vibrations (振动) as they're produced.

This could explain why so many people believe that singing or playing music to their plants helps them grow.

I had a plant that I used to wash the leaves once a week and sing to it, plant lover Heather Goodall told BBC News. It grew from being about 2 feet tall to 7 feet tall in just a couple of years.

So, does this mean we should start treating our plants like pets? Not necessarily, although perhaps it does mean we should give them more respect. I would like to see plants acknowledged more as the amazing, interesting, exotic living beings they are, and less as a mere source of human nutrition, Fatima Cvrckova, a scientist at Charles University in the Czech Republic, told BBC News.

Human speech contains more than 2,000 different sounds, from the common "m" and "a" to the rare clicks of some southern African languages. But why are certain sounds more common than others? A groundbreaking, five-year study shows that diet-related changes in human bite led to new speech sounds that are now found in half the world's languages. 

More than 30 years ago, the scholar Charles Hockett noted that speech sounds called labiodentals, such as "f" and "v", were more common in the languages of societies that ate softer foods. Now a team of researchers led by Damián Blasi at the University of Zurich, Switzerland, has found how and why this trend arose. 

They discovered that the upper and lower front teeth of ancient human adults were aligned(对齐), making it hard to produce labiodentals, which are formed by touching the lower lip to the upper teeth. Later, our jaws changed to an overbite structure(结构), making it easier to produce such sounds. 

The team showed that this change in bite was connected with the development of agriculture in the Neolithic period. Food became easier to chew at this point. The jawbone didn't have to do as much work and so didn't grow to be so large. 

Analyses of a language database also confirmed that there was a global change in the sound of world languages after the Neolithic age, with the use of "f" and "v" increasing remarkably during the last few thousand years. These sounds are still not found in the languages of many hunter-gatherer people today. 

This research overturns the popular view that all human speech sounds were present when human beings evolved around 300,000 years ago. "The set of speech sounds we use has not necessarily remained stable since the appearance of human beings, but rather the huge variety of speech sounds that we find today is the product of a complex interplay of things like biological change and cultural evolution," said Steven Moran, a member of the research team. 

Natural selection is the process by which one type of animal within a species develops well because of certain characteristics that make it more likely to live than others in its group. The history of the peppered moth(桦尺蛾) is an example of the natural selection process.

In nineteenth-century England, certain types of peppered moths were able to better blend (融合) into their surroundings. During that time period, great changes were happening in Great Britain. The Industrial Revolution was part of this change, and with it came air pollution. Natural selection usually takes hundreds or even thousands of years to occur. For the peppered moth, this process occurred relatively quickly .

At the beginning of the Industrial Age, most peppered moths in England were light-coloured and covered with black markings, although a few moths had dark-coloured wings. Because the light-coloured moths blended into the light-coloured bar k on the trees, they could not be easily seen by birds that would eat them. As the air grew more polluted, however, tree trunks (树干) became covered with soot (煤烟) and became darker. The light-coloured moths became easy for birds to see against the dark tree trunks. Since the dark-coloured moths now had the advantage, their numbers grew. Within 50 years, the peppered moth went from being mostly light-coloured to being mostly dark-coloured.

In the twentieth century, the air cleared up, and the peppered moth population changed again. As tree trunks lightened due to less soot in the air, light-coloured moths once again had an advantage. Their numbers increased as soot levels declined. Depending on their environment, the colouration of the moths helped them to be "naturally selected" to survive.