3. 在山顶吸入空气非常困难。

      air at the top of the hill.

2. 中国的人口比美国的多。

The population     that of the US.

1. 北京是中国最大的城市之一。

Beijing is    in China.

9. We must study hard to a our dreams.

10. A baby is usually about 3 kilos heavy at b .

8. We can spend some time doing some r work that you are interested in.

6. I have many friends,i some foreign people.

7. If you study really hard,you will s at last.

4. One adult elephant usually w 100 kilos.

5. Some endangered animals can easily die from i .

2. We should p the environment together.

3. Some scientists even want to face the f weather conditions.

1. The Sahara D is about 9600,000 square kilometers in size.

9. Our teacher came into the classroom with (兴奋) .

10. The (政府) should help the homeless people.