Hardly had I entered the room ______ it began to rain.

Hardly had I entered the room ______ it began to rain.
A、when
B、and
C、after
D、but
【正确答案】：A
【题目解析】：该题考查固定结构。hardly/scarcely/barely…when…= no sooner…than…意为“刚……就……”。