【求助】问个English问题
-Ihaveadifficulttime______homeword.Canyouhelpme?
-Sorry,Idon'thaveanyfreetime_______you.
A.todo,tohelp
B.doing,helping
C.todo,helping
D.doing,tohelp
该怎么选?
为什么选D?
这两句句式有什么区别么?