Life today is much     1     than it was hundreds of years ago, but at the same time, there are many new problems today. One of the biggest problems is pollution. Pollution comes in many different forms (形式). We see it, drink it and even hear it.

The pollution is getting more and more     2    . The more people there are, the more pollution there is. A long time ago, pollution wasn’t so serious,     3     there were not so many people, but now,     4     are polluting the whole world.

Many countries are making rules to fight against pollution. They stop people from using coal (煤炭) in houses and factories, and from putting dirty smoke into the air. They also     5     people to use their cars less and go to work by bus, bike or even on foot.

Look up at the sky at night. What can you see? Before electric lights, people could often see about 2,500 different stars. Now, light fills the skies over our cities. This is called light     1    . Because of it, people in cities can often only see about ten     2    !

Most of the time, light helps us. We can     3     because of it. It gives plants energy. But light isn’t always     4    . We need times of dark     5    . One hundred years ago, we had those times of dark. Now the night is like day. Some scientists are worried about     6     this light effects our health. These scientists are studying the effects of light pollution.

Other scientists are finding ways to     7     light pollution and make our lives better. For example, many street lights now have covers. The covers focus the light     8     the ground. They stop the light from going     9     into the sky. They also save energy. The covers are a     10     change, but they can     11     have a positive effect.