It was not until midnight ------- the snowcapped peak.A.that

It was not until midnight _______ the snowcapped peak.A.that they sighted B.that they did not si
It was not until midnight _______ the snowcapped peak.
A.that they sighted B.that they did not sight C.did they sight D.had they sighted
.求选项a和c解释谢谢.