状语从句练习
问题描述：
状语从句练习
he did not buy the book ,beacuse it was too expensive.
为什么在这里过去时还用buy ,而不用bought
答
buy是实义动词,其否定形式要用助动词 do not(过去时时用did not）,其人称和时态的变化都在助动词do oot上,而不需要改变buy.