【【【英语单句改错】】】急用!

【【【英语单句改错】】】急用!
1.We have waited for Tom for twenty minutes,but he hasn’t come yet.
2.The water is clean,and you can drink it without have it treated.
3.The box is so heavy and you can’t lift it.
4.Before James came to China he had learned some Chinese.
5.A fire was broken out last night in the neighborhood,but it had been put out before the firemen came.
6.The pen is good but it writes smoothly.
7.The two boys are running one after another.
8.The math problem is so difficult for me to work out.
9.China is an Asian country of a long history and a large population.
10.He is a good-trained sportsman.He broke the world record three times.
11.The novels by the famous writer are sold well.
12.It has rained heavily,and you must take your umbrella with you if you go out.
13.If I were you,I will take the job.
14.When I was young,my grandma often told me that a year had four seasons.
15.It is known that Taiwan is a place of the People’s Republic of China.
16.When doing homework,you should be careful and take it seriously.
17.Have you finished doing your homework already?
18.Everyone should do his duty in the work.
19.Learning English and to master it are two different things.
20.He talked long hours about the subject.I hope it will be over soon.