第一节：单项填空(共15小题，每小题1分，满分15分)

21．-Mr. Smith, I wonder if I could take Friday off?

　　　 -　　　 ? It’s a bit difficult with so many people away on holiday, you know.

　　　 A．How come 　　　　　　 B．Is it necessary

　　　 C．Where are you going　　　 D．Do you really have to