用所给词的适当形式填空。
1. If you work hard, you will be ___________(success).
2. Those workers spent ten months _____________(build) that bridge.
3. They often find it difficult ___________(learn ) English.
4. Pollution is one of the most serious _______ in the world (problem).
5. I had enough time_______(work) out that math problem.
6. The doctor told me to give up _______ (smoke).
7. I want _______(play) the piano in the evening.
8. We should stop_______(throw) about in public.
9. The knife _______(use) to cut things.
10. I think English is very _______(help) to know about the world.
1. successful 2. building 3. to learn 4. problems 5. to work
6. smoking 7. to play 8. throwing 9. is used 10. helpful