20. --- I rang you at about ten, but there was no reply.

　 --- Oh, that was probably _______ I was seeing the doctor.　

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

19. When we went boating on the lake that morning, it turned out fine, ______, very calm, without any wind.

A. except　　　 　　　　　 B. including　 　 C. but　　　　 　 D. besides

18. The area of Beijing City is about 　　　　　that of New York.　

　　 A. four times as much as　　　　　　　　 　　 B. as four times large as

　　 C. as four times greater than　　　　　　 　　　　 D. four times as big as