Not until they were introduced to each other ______ they had met at a dinner party. A. they realized

Not until they were introduced to each other ______ they had met at a dinner party.
A. they realized B. had they realized
C. they had realized D. did they realize
【答案】D
【解析】
【详解】考查倒装。句意：直到他们互相介绍认识之后，他们才意识到他们是在一次宴会上认识的。not until结构放在句首时, 其后的主句用部分倒装结构。此空“意识到”的时间发生在“被互相介绍”之后, 根据were introduced可知此空应用一般过去时。故选D。
【点睛】until的常用句式
(1)肯定句(延续性动词)+until+句子.
I will wait until he returns. 我一直等他回来。
肯定句(延续性动词)+until+名词或名词短语.
I waited for him until 12 o’clock.
(2)否定句(瞬间动词)+until+句子.
My mother had no idea of it until I told her.  
否定句(瞬间动词)+until+名词或名词短语.
I won’t leave until 12 o’clock.  
(3)not. . . until强调句
结构: It is/was not until +从句/表时间的词语+that +肯定句.
It was not until I told her that my mother had any idea of it.
(4)not. . . until倒装句(具有否定意义的词或短语在句首, 句子部分倒装)
结构: Not until+从句/表时间的词语+主句(倒装)
Not until 12 o’clock will I leave.