Question

 No sooner _____ themselves in their seats in the theatre _______ the curtain went up.

1. A.
   they have settled; before
2. B.
   had they settled; than
3. C.
   have they settled; when
4. D.
   they had settled;than

Answer 1

B
no sooner…than…,hardly…when…结构中，主句应用过去完成时的倒装结构。故选B。