It was not until the train was out of sight ________ they stopped waving their hands．

1. A.
   when
2. B.
   before
3. C.
   since
4. D.
   that

It was not until the train was out of sight________they stopped waving their hands.

A. when           B.before          C.since         D.that

 It was not until the train was out of sight      they stopped waving their hands.

A. when  B.before  C.since  D.that

It was not until the train was out of sight　　 they stopped waving their hands.

A. when B.before C.since D.that