Both men had just begun to swim towards the shore,为什么还要用过去完成时（had been）?
问题描述：
Both men had just begun to swim towards the shore,为什么还要用过去完成时（had been）?
Both men had just begun to swim towards the shore,when they noticed with dismay that the speedboat was moving in a circle.
答
因为后半句用过去式,过去的过去就是用过去完成