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Only after he had spent several nights working on the maths problem ________to  wonder whether the problem was wrongly set.

A．he began  B．that he began

C．he did begin  D．did he begin

Only after he had spent several nights working on the maths problem_______to wonder whether the problem was wrongly set.

A did he begin          B, he began          C, he did begin        D, began he

Only after he had spent several nights working on the maths problem      to wonder whether the problem was wrongly set．

A．did he begin      B．he began              C．he did begin               D．began he

Only after he had spent several nights working on the maths problem       to wonder whether the problem was wrongly set．

A．did he begin           B．he began            C．he did begin           D．began he