20．D。本句说明这个工人回答彼得的问题之前沉默了一会儿。A选项应用a moment； C选项表示某一点时间； D选项表示一段时间或一会儿，为正确选项。
21
A strange thing happened to Henry yesterday. He was on a bus and to __1__.
So he stood up and rang the bell. __2__ make sure the driver heard him,
he rang it twice, but the bus __3__ stop. And the conductor came and
shouted __4__ him.
The conductor was __5__ angry and spoke __6__ fast
that Henry didn’t understand __7__. The bus stopped at the next bus and
Henry got off. As he got off he heard someone said, “ I think he __8__ a
foreigner.”
When Henry got __9__, he told his wife about it.
“ __10__ times did you ring the bell?” his wife asked.
“ Twice,” said Henry.
“ Well, that’s the signal (信号) __11__ the driver __12__ on.” His wife explained, “only
the conductor __13__ to ring the bell twice. That’s why the conductor __14__
so angry!”
Henry nodded(点头). “ __15__,” he said.
