Question

I didn't know he came back ______ I met him in the street.

1. A.
   since
2. B.
   when
3. C.
   until
4. D.
   after

Answer 1

C
解析：
句意为“直到在街上见到他，我才知道他回来了”。not...until...是固定结构。意为“直到……才”。故选C。