4.Science is useful.It can benefit mankind.It is also dangerous.

Used by evil-doers it can bring harm to people.

3.The English language is difficult.

It is less difficult than the Russian language.

Its grammar is much simpler.

2.In Mr. Wang's house I met several college students.

All of them were engaged in revolutionary work.

例如：The gentleman lives here.

He is her brother.

合并为：The gentleman who lives here is her brother.

1.I was reading. She was writing.

8.A man must not wait for wonders to happen,　　　 the contrary,he must work hard　　　　 order to achieve them.

7.The Chinese working class varied its method and form of struggle　　　　 accordance　　　　 changing situations.

6.Though he is not sure 　　　　　success,he has made　 　　　his mind to take the examination.

5.I am interested　　　　 the study of mathematics,yet I am　　　　 a loss to solve this problem.

4.I am not well acquainted　　　　 your brother,　　　　 spite of the fact that you are a good friend of mine.

3.Many of my schoolmates are fond　　　　 playing basketball as well　　　 football.