Question

"________ I came into the office, the teachers were having a meeting．"

A. While
B. When
C. Once
D. Since

Answer 1

答案B
while引导的从句中动词常常是表示延续的动词或表示状态的连系词be; when表示“当……的时候”；once表示条件；since表示时间时意思是“自从……”。根据句意可知选B项。