21.A.I think it easy to work out the physic problem.

　 B.I think I _______ work out the physic problem _____________ .

　 C.________ easy ________ me _______ work out the physic problem.

20.A.I can’t finish the work on time if you don’t help me.

　 　B.I can’t finish the work on time ___________ __________ ___________.

　 　C.I can’t finish the work on time _________ you ________ me ______ ___________.

19.A.The book is so difficult that none of us ca read it.

　 B.The book is ________ difficult _________ us ________ read.

　 C The book _________ ________ ________ for us to read.

18.A.He seemed tired last night.

　 　B._________ __________ that _______ was tired last night.

17.A.Fish can’t live if there’s no water.

　 　B. Fish can’t live ___________ _________ water.

　 　C. Fish can’t live __________ there _______ water.

16.A.The boy is too young to go to school.

　 B. The boy is __________ young ________ he __________ do to school.

　 C. The boy isn’t _______ ____________ _________ go to school.

15.A.Mrs Green doesn’t like traveling by plane at all, I think.

　 B.I ____________ think Mrs. Green ___________ traveling a lot.

e.g. 1.She found him a very clever student.

= She found that he was a pretty clever student.

2.The gate is quite wide.　 Two cars can go through it at the same time.

= The gate is so wide that two cars can go through it together.

此类题目需要熟悉一些重要的句型和短语。例如：too… to …; so …that…; not… until…等。还要注意了解相关转换类型，如：without短语与if/ unless条件状语从句的转换；enough to …与so …that …的转换；too…to…,not…enough to…, so…that …not…的相互转换等。

Exercises:

14.A. Manuel usually goes to work by subway, sometimes he rides his motorcycle.

B. Manuel usually ________the subway to work, but at times he goes to work ______ motorbike.

13.A.Tom used a brush to clean his shoes.

　 　B. Tom ________ his shoes ____________ a brush.