Hundreds of years ago, life was harder than it is today. People didn't have modern machines. There was no modern medicine, either.

    Life today has brought new problems. One of the biggest is pollution. Water pollution has made our rivers and lakes dirty. It kills our fish and pollutes our drinking water. Noise pollution makes us talk louder and become angry more easily. Air pollution is the most serious kind of pollution to all living things in the world.

    Cars, planes and factories all pollute our air every day. Sometimes the polluted air is so thick that it is like a quilt (被状物) over a city. This kind of quilt is called smog.

    Many countries are making rules to fight pollution. Factories must now clean their water before it is thrown away, and they mustn't let dirty smoke go into the air.

    We need to do many other things. We can put waste things in the dustbin and do not throw them on the ground. We can go to work by bus with our friends in the same car. If there are fewer people driving, there will be less pollution.

    Rules are not enough. Every person must help to fight pollution.

B

    Many children spend a lot of time watching or playing with electronic media –from televisions to video games, computers and other devices（设备）.

    So, it is natural that parents should wonder about the time children spend looking at a TV or computer screen. Americans say “screen time” when they talk about any time children spend in front of an electronic device.

    Perhaps parents can stop worrying so much about screen time, at least for older boys and girls. In October 2016, the American Academy of Pediatrics (AAP) listed several suggestions for parents and child care workers. Here are some of the suggestions.

●Avoid digital media use in children younger than 18 to 24 months.

●For children aged 18-24 months, avoid letting the child watch media alone. And avoid using media as a way to comfort your child.

●For children two to five years of age, allow one-hour screen time on “high-quality（质量）programming” a day and watch it with your child.

●For children aged 6 and older, don't spend too much time using media. Also, make sure that screen time does not take the place of healthy sleep, exercising, doing homework and other activities.

●Make sure to have media-free time together as a family, such as dinner or driving. Also make some areas of the home media-free. Turn off you child's electronic devices an hour before bedtime.

D

    Almost every Chinese person can recite(背诵) the two lines of the famous poem, "Every grain on the plate comes from hard work". But sadly, many of us don't actually get the real meaning of these lines: Don't waste food.

    A CCTV program reported that the food Chinese people throw away every year is enough to feed 200 million people for a year. Do we have too much food? Absolutely not. According to the UN World Food Program, there were 925 million hungry people around the world in 2013, especially in developing countries. Six million children die of hunger every year.

    Chinese people are well-known for being friendly and generous. Many even feel that they lose face if their guests have eaten all the food on the table. Luckily, a number of people have realized the importance of saving food. What should we do in our daily lives to waste less food?

    ⒈ Don't order too much in a restaurant. Only order as much as you want to eat. If you cannot eat all the food you ordered, take the rest of it home.

    ⒉ Don't leave any food in your bowls while having meals.

    ⒊ Keep an eye on what food you have at home. Don't buy too much, especially for vegetables and fruit.

    Since the 1970s, scientists have been searching for ways to link the brain with computers. Brain-computer interface (BCI) technology could help people with disabilities send commands to machines.

    Recently, two researchers, Jose Millan and Michele Tavella from the Federal Polytechnic School in Lausanne, Switzerland, demonstrated(展示) a small robotic wheelchair directed by a person's thoughts.  In the laboratory, Tavella operated the wheelchair just by thinking about moving his left or right hand. He could even talk as he watched the vehicle and guided it with his thoughts.

    "Our brain has billions of nerve cells~ These send signals through the spinal cord(脊髓) to the muscles to give us the ability to move. But spinal cord injuries or other conditions can prevent these weak electrical signals from reaching the muscles," Tavella says. "Our system allows disabled people to communicate with external (外部的) world and also to control devices."

    The researchers designed a special cap for the users. This head cover picks up the signals from the scalp(头皮) and sends them to a computer. The computer interprets (translate) the signals and commands the motorized wheelchair. The wheelchair also has two cameras that identify (find or discover) objects in its paths. They help the computer react to commands from the brain.

    Professor Millan, the team leader, says scientists keep improving the computer software that interprets brain signals and turns them into simple commands. "The practical possibilities that BCI technology offers to disabled people can be grouped in two categories: communication and controlling devices. One example is this wheelchair. "

    He says his team has set two goals. One is testing with real patients, so as to prove that this is a technology they can benefit from. And the other is to guarantee that they can use the technology over long periods of time.

    Solar storms shake Earth's magnetic field(磁场). They not only influence human technology, but also animals, reported Forbes.

    Studies show that many animals use changes in Earth's magnetic field to find directions. These changes provide the animals a general compass(指南针) for south and north. Animals can also use them as landmarks.

    For example, scientists have found special cells in part of a bird's eye nervous system(神经系统). They seem to react to changes in the magnetic field.

    Some fish species, like the common trout，have cells with magnetic sensors in their nasal cavity(鼻腔). In 1994 "magnetic sense" was also discovered in sea turtles.

    Some whale species may use magnetic sense to navigate (导航) the oceans. A dysfunction of this sense may explain the still mysterious beachings (动物搁浅). Sometimes several hundred animals, such as whales and dolphins, are driven out of water along beaches. They usually can't breathe under their own weight and die slowly.