15. The reason ___ he can’t come is ______ he has to work late.

　 A. because; that　 　B. that; that　 　C. why; that　 　D. why; because

14.Though I have no idea _______ the new film is about, I know it is popular with all who have seen it.

A. whether　　　 B. why　　　　　 C. that　　　　　 D. what

13. They desired that they_______ the right to vote.

A. had　　 　　B. have　　　 C. are　　　 D. were

12. The professor explained this theory so clearly that this phenomenon was easy enough ________.

A. for us to work out　　 B. working out　　

C. for working out　 　　D. to working out