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.

    We would like to wish all our readers a wonderful winter break. Our January magazine is now in the shops and available digitally. We're looking forward to sharing more adventures and discoveries with you in 2018, including:

    At a crossroads in the Atlantic

    As the population of Ascension Island rises up to mark the 200th anniversary of British rule, Fred Pearce wonders what the future might have in store for this strange part of land.

    Photostory: On the road again

    A selection of images from an exhibition opening this month at the Royal Geographical Society go hand in hand with M. Aurel Stein's early 20th century photographs of the Silk Road.

    Dossier: Going underground

    Mark Rowe discusses the role that carbon storage can play in the global effort to reduce carbon dioxide emission (排放).

    Net loss

    Kit Gillet reports from the Gulf of Thailand, whose fisheries (渔场) have been almost destroyed by the commercialization of the Thai fishing industry.

    And don't forget...a round-up of the latest geographical and climate science news; a hot spot focus on Turkey; advice on taking photographs in Antarctica; an interview with Lucien Castaing-Taylor, professor of visual arts at Harvard; plus lots, lots more...

    Buy your copy now, click here and save up to 35% or call+44

    Palaces are known for their beauty and splendor, but they offer little protection against attacks. It is easy to defend a fortress (堡垒),but fortresses are not designed with the comfort of a king or queen in mind. When it comes to structures that are both majestic and well-defended, the classic European castle is the best example of design. Across the ages castles changed, developed, and eventually fell out of use, but they still command the fascination of our culture.

    Castles were originally built in England by Norman invaders. In 1066. As William the Conqueror advanced through England, he defended key positions to secure the land he had taken. The castles he built allowed the Norman lords to draw back to safety when threatened by English rebellion. Castles also served as bases of operation for offensive attacks. Troops were summoned to（召集）, organized around, and deployed (部署) from castles. In this way castles served both offensive and defensive roles in military operations.

    Not limited to military purposes, castles also served as offices from which the lord would administer control over his kingdom. That is to say, the lord of the land would hold court in his castle. Those that were socially beneath the lord would come to report the affairs of the lands that they governed and pay tribute to the lord. They would address conflicts, handle business, feast, and enjoy festivities, In this way castles served as important social centers in medieval England. Castles also served as symbols of power. Built on important and noticeable sites overlooking the surrounding areas, castles constantly appeared in the background of many peasants' lives and served as a daily reminder of the lords strength.

    Now, castles no longer serve their original purposes. However, the remaining castles receive millions of visitors each year from those who wish to experience the glory of a time long passed.

    The English language has a lot of words which can be used in many different ways and in many different expressions.

    One such example is the word matter. In fact, matter can mean just about anything. It could be one of the most useful words in the English language.

    Let's get to the heart of the matter—a matter of principle (原则).

    If someone says that you owe (欠) him $50, but you don't, a friend might say, "Well, you could pay him the $50. It's not that much money. Then you won't have to hear him say it anymore." But if you do not owe him the money, do not pay him the money. It's a matter of principle.

    There is another way to use the word matter. But be careful with your choice of words.

    If you ask someone, "What's the matter?" it shows you are worried about the other person. But saying, "What's the matter with you?" has a completely different meaning. And it usually sounds rude (粗鲁的). In fact, when you say, "What's the matter with you?" you are suggesting that the person did something wrong or stupid.

    Another expression that could sound rude is to say, "It doesn't matter to me." Here, it depends on the context, and how you say it.

    Let's say you tell someone that a friend just got a big raise at work. That person answers with, "It doesn't matter to me." Here, it means he or she does not care. And it sounds rude.

    But saying, "Oh, you pick where we eat dinner. It doesn't matter to me." does not sound rude. In this situation, "it doesn't matter" shows you are easy-going (随和的).

    No matter how you look at it and what you say, matter is a very useful word. And it's only a matter of time before you will become an expert on the use of matter.

    With the possible exception of equal rights, perhaps the most controversial issue across the United States today is the death penalty. Many argue that it is an effective deterrent (威慑) to murder, while others maintain there is no convincing evidence that the death penalty reduces the number of murders.

    The principal argument advanced by those opposed to the death penalty, basically, is that it is cruel and inhuman punishment, which is the mark of a brutal society, and finally that it is of questionable effectiveness as a deterrent to crime anyway.

    In our opinion, the death penalty is a necessary evil. Throughout recorded history there have always been those extreme individuals in every society who were capable of terribly violent crimes such as murder. But some are more extreme than others.

    For example, it is one thing to take the life of another in a fit of blind rage, but quite another to coldly plot and carry out the murder of one or more people in the style of a butcher. Thus, murder, like all other crimes, is a matter of relative degree. While it could be argued with some conviction that the criminal in the first instance should be merely separated from society, such should not be the fate of the latter type murderer.

    The value of the death penalty as a deterrent to crime may be open to debate. But the overwhelming majority of citizens believe that the death penalty protects them. Their belief is strengthened by evidence which shows that the death penalty deters murder. For example, from 1954 to 1963, when the death penalty was consistently imposed in California, the murder rate remained between three and four murders for each 100,000 population. Since 1964 the death penalty has been carried out only once, and the murder rate has risen to 10.4 murders for each 100,000 population. The sharp climb in the state's murder rate, which began when executions stopped, is no coincidence. It is convincing evidence that the death penalty does deter many murderers. If the bill reestablishing the death penalty is banned, innocent people will be murdered—some whose lives may have been saved if the death penalty were in effect. This is literally a life or death matter. The lives of thousands of innocent people must be protected.

If you have a passion for music, art, history and more, indulge it on a Yoyo Odyssey Cultural Tour!

How we travel can make the difference between just visiting a place, or really experiencing it from the inside out, which is why Yoyo has created its new Odyssey Cultural Tours collection.

These small-group, luxury tours offer a deep div e into history, art, music, literature, dance and astronomy, while enjoying everything that a destination has to offer, from exceptional places to stay to the best of local food.

Each holiday has the service of a Yoyo tour manager and we'll take care of you every step of the way, providing a VIP car service to your UK departure point for overseas trips, flights and transfers, all transports to accommodations, travel insurance and much more.

For music lovers; Yoyo has partnered with the Royal Academy of Music to create unique short breaks in London with concerts by talented young musicians from the Academy.

You'll be in expert hands-each tour is accompanied by a specialist in their field who's skilled at sharing their expertise through insight-packed talks throughout the holiday. Backstage, behind-the-scenes visits give a fascinating perspective on new places as well as cities that you may already know and love, all in the stimulating company of like-minded travellers.

ABC Music readers will receive an exclusive 5 per cent discount on all Yoyo Cultural Odyssey Tours-just quote the code ‘ABCR' when booking. To find out more please visit yoyo.uk/COT.