改错 1) He is not only a good pianist,but also a good singer as well(as well去掉).2.This pretty actress keeps appearing in TV serials repeatedly（repeatedly去掉）.3.As a rule,students are usually not (usually和not交换位置)allowed to take books out of this reading room.
4.According to the speaker,it is obvious that the responsibility system has helped to increase production and（加上that） he has no doubt about it.
5.One reason why people are well informed in this country is because of(because of改为that,因为当reason优质主语时,它的表语用that不用because) the fact that there are many newspapers which can easily be bought or subscribed to.
6.Statistics show that in the decade from 1980 to 1990 enrollments at this school doubled:in 1990 there were twice as many students as in 1980.
7.There are so many inexperienced unskilled workers without training(training改为being trained) in a particular job that production of the factory has been affected.
8.There are about 50 patients or so(去掉or so或去掉前面的 about) in this ward,among whom many are being given acupuncture treatment.
9.His name（his name改为He或者去掉is） is called James Williams.10.Whatever he does,he works seriously (seriously去掉)with great care,and does his best so as to do it well.
11）I am quiet（改为quite） jealous of your opportunity to study at such a famous university.
12) The essay is poorly organized,(加上because)there is no central idea.
13) There are a number of students who want to join the drama club.He was kind enough to let me share the same umbrella with him.
14.Zhao was the person who was elected（加上as） the representative of the class by the whole class.
15.At the present time I am taking the course of World History and in addition（加上to） a course in geography too(去掉too).15.The plane circled around the airport for about（去掉about） ten minutes or so and then disappeared and could no longer be seen.
16.What I am trying to say is that in my opinion he has not done his work very well and (加上that)it needs improving.
17.I would like you to consider the question of whether or not （去掉or not）you will publish your recent article on women scientists in China in our journal.
18.Owing to the fact that he had missed many lectures,he was aware that it would be possible for him to fail the exam.
19.You must first work out an outline for your paper,and then (then去掉)after you have done that,you need to collect all kinds of material to support your point of view.