Not until his mother came back .
A. he began to do his homework
B. had he began to do his homework
C. he had begun to do his homework
D. did he begin to do his homework
网友回答
A. he began to do his homework
B. had he began to do his homework
C. he had begun to do his homework
(答案→)D. did he begin to do his homework
解析：考查倒装句：not until放在句首的时候，主句用部分倒装，答案在BD里面选择，句意：直到他妈妈回来，他才开始做作业。可知是妈妈回来后，他做作业，不是过去的过去的动作。选D。