Question

When did you leave the bus station? （）I saw him get on the bus and sit down.

A.Before B.After C.Since D.Until

Answer 1

D. Until, 这是一个省略的回答，完整的回答句子应该是I didn't leave the bus station until I saw him get on the bus and sit down.
所以答案最合适的是D。

Answer 2

D.
你什么时候离开的公交车站？
直到我看见他上了车并且坐下。

追问

确定么？

Answer 3

A.
你什么时候离开的公交车站？是在我看见他上车坐下后。