[单项选择]Hundreds of years ago, life was much harder than it is today. People didn’t have modern machines. There was no modern medicine, (41) .
Life today has brought new (42) . The biggest one is pollution. (43) 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 (44) easily. Air pollution is the most serious kind of pollution. That’s bad to all (45) things in the world.
Cars, planes and factories all pollute our air every day. (46) the polluted air is so thick that it is like a quilt(被子) over a city. This kind of quilt is called smog(烟雾).
Many countries are making rules to (47) pollution. Factories must now clean their water before it is thrown away. They mustn’t blow dirty into the air.
We need to do many (48) things. We can put waste things in the dustbin and not throw it on the ground. We can go to work