Question

___ he was out of the room,he turned back and knocked at the teacher's door again.

A Before
B Since
C As soon as
D Unitil
说明原因

Answer 1

C
AD句意不通 ， B时态不符（应该是since+完成时）

这句话翻译过来大概就是他一出老师的办公室就马上回来又重敲了