Sentence Correction (SC) | Re: By the mid-1700s, when it began a concerted effort to prevent famine a

normally if the time in main clause in in the past, the time in subordinate clause also in the past but it can be in present.

this case is odd because time in subordinate clause seems go before time in main clause.

this problem shows that main clause can be in past perfect and subordinate clause can be in simple past.

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