這是根據(jù)語境確定時態(tài)的一道妙題

請看題：

—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】此題應(yīng)選 B。這是一道很好的測試時態(tài)的語境題。此題的情景是：一方提醒另一方不準(zhǔn)抽煙，對方表示歉意并說自己不知道。這里的“不知道”顯然是指對方“提醒”之前“不知道”(所以用過去時態(tài))；假若用一般現(xiàn)在時，則指在對方提醒之后還仍然不知道，這不是很荒唐嗎?

在做時態(tài)試題時，要特別注意上下文的語境：

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