What the old man ( )have a great effect on him.

问题描述:

What the old man ( )have a great effect on him.
A does B does do C does does D do does

同意楼上观点.应该选C: 第一个does做主语从句What the old man does的谓语动词,第二个does是对主句谓语动词have的强调,表示“的确对他有巨大的影响”.