问题
选择题
We were about to leave the classroom _____ it began to rain.
A．while
B．when
C．as
D．before
答案
B
be about to do sth. when "…正要干某事，这时…"。
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We were about to leave the classroom _____ it began to rain.
A．while
B．when
C．as
D．before
B
be about to do sth. when "…正要干某事，这时…"。