请看一道题：

It was not __________ he took off his dark glasses __________ I realized he was a famous singer.

A. when，that                        B. until，that                        C. until，when                        D. when，then

此题选B。考查 not...until 的强调结构，其基本句型为：

It is (was) not until (时间状语) that 从句(不用否定)

他妻子走了之后他才来。

正：He didn’t come until his wife left.

正：It was not until his wife left that he came.

直到雨停他们才出发。

正：They didn’t start until the rain stopped.

正：It was not until the rain stopped that they started.

请做以下各题(www.yygrammar.com)：

1. It was not until midnight __________ the noise of the street stopped.

A. that                 B. this                   C. since            D. at which

2. It was not _________1920 _________ regular radio broadcast began.

A. for，that         B. until，that         C. for，when     D. until，when

3. It was not _________ you had explained how _________ I managed to do it.

A. for，that          B. until，that         C. for，when      D. until，when

答案：1. A      2.      B 3. B