问题
选择题
Someone knocked at the door he was doing his homework.
A．after
B．when
C．until
D．as soon as
答案
答案：B
题目分析：句意：有人敲门，他正在做作业。After在……之后；when当……的时候； until直到； as soon as一……就。结合前后句子意思可知该选B。
搜题请搜索小程序“爱下问搜题”