Question

【题目】Last Monday, I was chatting online _____, before I knew it, our manager came in and stood
behind me.
A.until
B.when
C.as
D.so

Answer 1

【答案】B
【解析】句意：上周一，我正在网上聊天，在我注意到之前，我们经理就走进来站在我身后了。这里用连词 when表示一件事发生时，另一件事发生了。故选B。