They spent half an hour (pack)their bags 用适当形式填空 过去完成时
问题描述:
They spent half an hour (pack)their bags 用适当形式填空 过去完成时
答
They spent half an hour packing their bags.
spend time (in) doing sth 是固定结构(in往往省略),这里不用过去完成时.
过去完成时用来表示“在过去的某个动作之前已完成的动作,也就是”过去的过去”.
When we arrived at the station, the train had already left.