11. With the d________ of economy, people’s living standard is better and better now.

10. Water ________ (存在) in three forms, which are liquid, gas and solid.

9. The earth is one of the nine p________ which go around the sun.

8. Oceans cover two thirds of the s________ of the earth while land covers one third of it.

7. As a middle school student, you may find you are growing up ________ (渐渐地).

6. To work out this problem, we have tried many m________.

5. There is a v________ wind outside and the snow is so heavy.

4. There is a big underground railway ________ (系统) in London, which is good for travellers.

3. By the time they reached the top of the mountain they were e________.

2. It is possible to ________ (繁殖) these bacteria in the laboratory.