I had no sooner closed the door ______ somebody started knocking

I had no sooner closed the door ______ somebody started knocking on it.
A、as
B、before
C、than
D、when
【正确答案】：C
【题目解析】：no sooner…than…”是固定搭配，意为“刚……就……”，表示一件事紧接着另一件事发生。一般情况下，后面的从句用一般过去时，前面的主句用过去完成时，例如：I had no sooner sat down than the telephone rang．我刚一坐下，电话铃就响了。when须和hardly(scarcely，barely)连用，意义同上，例如：I had hardly closed the door when somebody started knocking on it．我刚关上门就有人敲起门来。根据结构可知C为正确答案。