They are too busy.They have to___Mrs.Green___their housework

D
A.错.pay sth for sb ,没有pay sb ,根据语意,直接排除
B.Mrs.Green是人,你想用人做什么?补充一下,sb used to do sth某人过去常常做某事,sb be used to doing 某人习惯于做某事 ,sth be used for sth 某物被用来...
C,同上 spend 时间(in)doing sth ,用法错误
D,take sb to do sth 带某人去做某事
to do their housework 去做家务.

A。花钱买某物
B.be used for某物用来做。。。
C.spend...on花多长时间做某事
D.take...to带某人做某事
依题意，D对

D take sb. to do sth