It was not until midnight____the camp site as planned.

问题描述:

It was not until midnight____the camp site as planned.
A.that they reached
B.were they reaching
C.did they reach
D.as they were reaching
请说明理由.

A
是强调句.
They reached the camp site as planned.强调时间:
It was not until midnight that they reached the camp site as planned.