答案：
1、We often correct each other's mistakes in our exercises in class.
2、She speaks English with a good pronunciation.
3、The key to his success is to work hard.
4、Tom is an excellent student.
5、It can be exciting to get stamps which you do not have yet.
7、A careless driver is a danger to the public.
8、Will you let me walk under your umbrella?
9、He has been driving a truck for years and never had an accident.
10、We should protect wild animals in danger.
11、We have had some help from the government.
12、We brought along pieces of old bread and fed the birds.
13、Pay attention to your spelling.
14、Climbing the first hill took us half an hour.
15、he usually goes to work by bike except on rainy days.
16、Julia was busy preparing her speech.
17、Let me take your temperature first.
18、I told them to be quiet and go to sleep.
19 、Air pollution is becoming a serious problem.
20、Westerners are not used to eating with chopsticks.
21、I got in touch with him immediately after I received the letter.
22、Smoking is harmful to our health.
23、The police have put up signs to warn people off this area.
24、He learned this lesson the hard way — from his own personal experience.
25、Don't laugh boy. This is serious.
26、Once this difficulty is overcome, other problems will be easy to solve.
27、I think it a good idea to stop smoking in public places.
28、Smoking is the biggest cause of death and disease.
29、In the afternoon it rained suddenly.
30、He gave his life to saving animals in danger.
