因为前边的句子是The time was a quarter past five in the afternoon.And I was driving along the
road to fetch my daughter from her school.Our plan had been to go swimming
together.所以 后面的句子 用过去完成时 表示是在 a quarter past five以前 发生过的事 I可以跟时间点 at about 4 o’clock连用 i had finished work at about 4 o’clock and then gone to the post
office.