第二部分英语知识运用（共两节，满分25分）
第一节 单项填空（共5小题；每小题1分，满分5分）
请认真阅读下面各题，从题中所给的A、B、C、D四个选项中选出最佳选项，并在答题卡上将该项涂黑。
21．—Did Jack come back early last night?
—Yes．It was not yet eight o’clock ______ he arrived home．
A．before B．until C．when D．after
22．—What did the manager say at yesterday’s meeting?
— So you______ to him carefully．
A．won’t listen B．weren’t listening
C．hadn’t listened D．haven’t listened
23．Not until World War II ______ to use new chemical techniques to purify penicillin．
A．they managed B．that they managed
C．did they manage D．they didn’t manage
