Like humans, dogs donate blood too, and not every dog can donate blood. The dogs are screened(检查) for health first. Dogs must have the correct blood type, weigh at least 55 pounds and be younger than 8 years old. They may donate three or four pints(品脱) a year, which can help animals that are suffering from illnesses like cancer or an accident like being hit by a car. One pint can save up to three dogs.

    Owners volunteer their pets for the short procedure (程序), which requires no sedative, a kind of medicine given to calm him or her down. It's the dog that finally chooses to lie still and give. If the dogs want to get up and leave, they can.

    Sandy Lucas brought her 7-year-old black German shepherd, Rains, to the bloodmobile(流动血站) when it was parked at her small village. Sandy said she wouldn't have troubled herself with highway traffic and city parking problems to take the dog to Penn Vet's animal hospital in downtown Philadelphia, which is twice as far as her home. But the bloodmobile made it easy to find out if Rains could donate. "I was very, very excited that she had the right blood that was needed to help another dog out," said Sandy. "We'll surely do it again."

    In today's world, almost everyone knows that air pollution and water pollution are harmful to people's health. However, not all the people know that noise is also a kind of pollution, and that is harmful to human health, too.

    People who work and live under noisy conditions usually become deaf. Today, scientists believe that 10% of the workers in Britain are becoming deaf because of the noise where they work. Many of the workers who print newspapers and who weave cloth (织布) become deaf. Plenty of people living near airports also become deaf. Recently it was discovered that many teenagers in America could hear no better than 65-year-old persons, because these young people like to listen to pop music and most of pop music is a kind of noise. Besides, noise which is produced by jet planes or machines will make people's life difficult and unpleasant. It can make people ill or even drive them mad.

    It is said that a continuous noise of more than 85 decibels (分贝) can cause deafness. Now the governments in many countries have made laws to control noise and make it less than 85 decibels.

    In China, the government is trying to solve not only air and water pollution problems but also noise pollution problems.

    It's hard to turn down a tasty banana. They taste good and you don't have to wash them before eating them. However, British scientists say that the fruit may disappear by 2050.

    One reason for this is climate(气候) change. Scientists at the University of Exeter collected data(数据) from 27 countries and regions that produce 86 percent of the world's bananas. They found that climate change has improved growing conditions in 21 of these countries. In the past 60 years, the average yield(平均产量) has reached 1.37 tons of bananas per hectare(公顷).

    However, if temperatures keep rising, this advantage will disappear. Ten of the countries, including India, the world's biggest producer of bananas, will produce fewer bananas. By 2050, the fruit may die out.

    Shouldn't bananas grow more easily if it's hotter outside? In fact, the perfect temperature range for growing bananas is between 24 and 32 C. If temperatures get too high, they will stop growing.

    Diseases are another danger to bananas. Unlike other crops, the bananas we grow come from shoot cuttings(茎段) rather than seeds. This means that all banana plants have the same genotype(基因型). In other words, if a disease is able to kill one plant, it could kill them all.

    One serious disease is called Panama. Caused by fungus(真菌) in the soil, it spreads easily. It has spread across South Asia, Africa, the Middle East, and Australia. If one banana plantation(种植园) suffers from the disease, it will take 30 years until it is able to grow bananas again. Scientists have yet to find a cure for this disease.