题目内容：

April 22 is Earth Day. Everyone on Earth should care about and protect the earth!

The earth has warmed by about 1°F (华氏度) over the past 100 years, but why and how?

Well, scientists are not quite sure. Maybe the earth gets warmer and warmer on its own. But many scientists say that people are doing many things which makes the earth warmer.

First, greenhouse effect (温室效应) is a very important reason for the change of the earth. People give out too much energy into the air every year. It makes the earth warmer. Climate (气候) change is another important reason. Sometimes it becomes too hot and sometimes too cold. Sometimes there is too much rain and sometimes too little. The change of the climate makes the earth warmer. In turn, the warmth of the earth changes the climate, too.

When the earth becomes warmer, there may be more rain and a rise in sea level. It will affect the growth of plants, animals and people. On a Pacific island, 100 people have to move to higher ground because the sea is rising. These people can no longer live on the coast. Before that, two islands without people went underwater in 1999. Scientists say that the seas can rise by nearly one metre by 2100.

People can affect the earth's air, land and water. As for us, we can do many things to protect the earth. For example, we can use fridges less. We can tell more people about protecting the earth.

1.Earth Day is probably set for people to ______.

A．learn more about the earth                B．make full use of the earth

C．take better care of the earth.              D．study the warmth of the earth

2.We can infer (推断) from the passage that the reasons for the warmer earth are

______ now.

A．not very clear      B．completely secret   C．well known        D．not given yet

3.Greenhouse effect comes from______.

A．sea rising          B．climate change     C．nature's unbalance  D．people's activity

4.The passage mainly tells us that ______.

A．there is more rain now                   B．we should protect the earth

C．we must stop pollution                   D．sea level is getting higher