题目内容：

 

1.We are trying__________(work) hard at all the subjects.

2.There used to _________(be) a lot of manatees. But now there are few.

3.What was the air pollution__________(cause) by?

4.Have you ever__________(throw) away things you don't like to use?

5.I have also__________(set) up a website to sell clothes online.

6.Mark__________(work) in China for 10 years and now he teaches Chinese in Britain.

7.What would happen if he__________(go) back home late?

8.Can the book be__________(bring) back to my room?

9.--Why not__________(buy) John a toy car for his birthday?

--Good idea! He is crazy about cars.

10.The math problem is so hard. I really don't know how________(do) it.