Question

I don’t remember how many years ago ________ people began to grow crops．

A. it was when
B. was it that
C. it was that
D. was it when

Answer 1

答案A
该句型中的when引导的是一个时间状语从句，主句中的it指时间，表语由具体的时间充当。常译为“当……的时候；是……”。