问题描述：
As ( ),they were waiting for us at the airport.A.plan B.planned
As ( ),they were waiting for us at the airport.
A.plan B.planned
C.planning D.being planned
请问为什么选B
As ( ),they were waiting for us at the airport.
A.plan B.planned
C.planning D.being planned
请问为什么选B
问题解答：
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