It was not until midnight they reached the camp site.
A. that
B. when
C. while
D. as
网友回答
(答案→)A. that
B. when
C. while
D. as
解析：句意：他们直到半夜才到达宿营地。本句考查强调结构，可以还原为：They didn’t reach the camp site until midnight. 这是含有until引导状语从句的强调句型。当强调 until从句部分时，应注意把not一起提前。即：It is/ was not until + 被强调部分 + that + 其它部分。