It was not until the boat was out of sight ________ their hands．

1. A.
   that they stopped waving
2. B.
   did they stop waving
3. C.
   they don't stop waving
4. D.
   had they stopped waving

河北省衡水中学2011年第二学期第一次调研考试

It was not until the boat was out of sight _____________ their hands.

A. did they stop waving　　　　　　 B. that they stopped waving 　　　　　　　　

C. they don't stop waving　　　　　　 D. had they stopped waving