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

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

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

1. A.
   it was when
2. B.
   was it that
3. C.
   it was that
4. D.
   was it when

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

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