2020湖南普通专升本英语语法：not...until用于强调句型的用法

not...until用于强调句型的用法
有这样一道考题，其中涉及了not…until…句型：
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(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：
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