--,we had to hire a taxi,for we missed the last bus.

A 有语法错误,除非说：As it was pretty late
由于已经很晚的逻辑主语是It(指时间）,而句子的主语是we,所以如果选D,逻辑主语就不一致了!
C 项本身没问题,但如果后接__,we had to hire a taxi,for we missed the last bus这个题干,就不知道是什么句子类型了!
选B 是独立主格结构做原因状语
再问： As it was pretty late 什么意思 那个As
再答： 因为---引导原因状语从句
As it was pretty late “【由于】已经很晚了”