修改时间：2021-05-20 浏览次数：363 类型：同步测试
Miss Richards was a teacher at a school for boys and girls. She 1 chemistry and physics from the lowest to the highest classes in the 2. Sometimes the new classes 3 rapidly, but sometimes they were very 4, and then Miss Richards had to 5things many times.
One year, the first class had been studying chemistry for several 6 when Miss Richards suddenly asked, "What is water? Who knows? 7 up!"
There was silence for a few seconds, and Miss Richards felt sad, but then one boy 8 his hand.
"Yes, Dick?" said Miss Richards encouragingly. He was not one of the brightest children in the class, so she was 9 that he could answer.
"Water is a liquid which has no 10 until you wash your hands in it, Miss. Then it turns black, "the boy replied with great confidence.
Germs are always in dirty water. When you look at dirty water under a microscope, you will see them in it. So your parents will not let you drink dirty water.
Germs are found not only in dirty water, they are also found in air and dust. If you cut your finger, and if some of the dust goes into the finger, it will become big and red, and you will have much pain in it. Sometimes they will go into your body and you will have pain everywhere.
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.
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