Hundreds of years ago, life was much harder than it is today, people did not 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 affects our drinking water. Noise pollution makes us talk louder and become angry more easily. Air pollution is the most serious kind of pollution. It affects every living thing in the world. Cars, planes and factories all pollute our air every day. Sometimes the pollution is so thick that it is like a quilt(被子) over a city. This kind of quilt is called smog. Many countries are making new laws to fight pollution. Factories must now clean their water before it is thrown away; they mustn’t blow dirty smoke into the air. We need to do many other things. We can put waste things in the dustbin and not throw them on the ground. We can go to work by bus or with our friends in the some car. If there are fewer people driving, there will be less pollution. Laws are not enough. Every person must help to fight pollution. 49. Life was harder hundreds of years ago because____________. A. the weather was bad             B. there were no cities C. people had no modern machines    D. people couldn’t make machines 50._______ makes the rivers and lakes dirty. A Swimming.   B Polluted water   C. Growing population   D. Warmer weather 51.More and more people become angry easily because __________. A. they can’t get enough money           B. They are often hungry C. there’s much traffic on the roads        D. there’s much noise around them 52 The writer of the passage thinks__________. A. everyone should do something to fight pollution B. all the laws can stop factories going on polluting C few countries can stop the air and water being polluting D. people have to live in the polluted air..