I got up early that morning but I so because I had no work to do.A. mustn’t have doneB.

问题补充：

I got up early that morning, but I so because I had no work to do.

A. mustn’t have done

B. didn’t need to do

C. needn’t have done

D. can’t have done

答案：

A. mustn’t have done

B. didn’t need to do

(答案→)C. needn’t have done

D. can’t have done

解析：needn’t have done表示“过去不必做而做了某事”，若表示“不必做某事（且实际上未做）”则用“didn’t / don’t / doesn’t need to.”