78. The question isn’t　 easy.　 I can't answer it.　 (合并为一个复合句)

The question is______ difficult ______ I can’t　 an­swer it.

77. Both of us have been to the Great Wall,　　 (改为否定句)

______of us______been to the Great Wall.

　 按括号内要求改写句子。

76. You should finish your homework in an hour.　 (改为祈使句)

______your homework in an hour,　 _______.

40. China has______the WTO for some years.

A. taken part in　　　　　 B. joined

C. been a member of　　　　　 D. entered

39. Lucy’s mother told her to come back earlier, ______.

A.　 so she does　　　　 B.　 so it is

C.　 so did she　　　　　 D.　 and so she did