请看题： —Excuse me, sir. Smoking is not allowed here. http://yingyu.chazidian.com —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