一道英文题目(初一上Units4-5),如下【见问题补充】:
Hismotheralways_____him_____totheteacherforhelp.
A.let,askB.lets,askC.lets,toask
标答:选【】
原因:________________________________(详细说明)
我姐说“let”不能加“s”,可这里三单现(加/不加),请选择并说明理由:____________________________
到底是"letSbdoSth"还是"letSbtodoSth"?区别?_________________________________