阅读下面材料，在空白处填入适当的内容（1个单词）或括号内单词的正确形式。
Nowadays more and more people are using modern traffic and modern communication means. The world ____ (it) is becoming much smaller. So life today is much easier than it was ____ (hundred) of years ago. but it has brought new ____ (problem). One of the biggest problems is pollution. To pollute mean to make things dirty. Pollution comes ____ many ways. We see it, smell it, drink it and even hear it.
Air pollution is still the most serious. It's bad to all living things in the world, but it is not the ____ (bad) one kind of pollution. Water pollution kills our fish and pollutes our drinking water. Noise pollution makes us become angry more ____ (easy).
Pollution by SO2 is really the most dangerous problem of air pollution. It is ____ (cause) by heavy traffic. It is true that ____ there are fewer people driving, there will be less air pollution.
The earth is ____ (we) home. We must take care of it. That means ____ (keep) the land water and air clean. And we must take care of the rise in pollution at the same time.
