根据语境确定时态的好题
请看题：
—Excuse me, sir. Smoking is not allowed here.
—Oh, sorry I __________.
A. don’t know B. didn’t know
C. haven’t known D. can’t know
【分析】此题应选 B。这是一道很好的测试时态的语境题。此题的情景是：一方提醒另一方不准抽烟，对方表示歉意并说自己不知道。这里的“不知道”显然是指对方“提醒”之前“不知道”(所以用过去时态)；假若用一般现在时，则指在对方提醒之后还仍然不知道，这不是很荒唐吗?
在做时态试题时，要特别注意上下文的语境：
1. —We could have walked to the station; it was
so near.
—Yes. A taxi ________ at all necessary.
A. wasn’t B. hadn’t been
C. wouldn’t be D. won’t be
2. —Your phone number again? I ________ quite catch it.
—It’s 7226109.
A. didn’t B. couldn’t
C. don’t D. can’t
3. —Can I help you，sir?
—Yes. I bought this radio here yesterday，but
it _________ work.
A. didn’t B. won’t
C. can’t D. doesn’t
4. —Alice，why didn’t you come yesterday?
—I _________，but I had an unexpected visitor.
A. had B. would
C. was going to D. did
答案：1. A 2. A 3. D 4. C