题目

A lot of children are used to ________ their time ________ up by their parents and they simply don't know ________ with their spare time themselves. A . have; full; what to deal B . having; filled; how to do C . have; filling; how to deal D . having; filled; what to do 答案：D已知函数（a为常数）在x＝处取得极值，则a的值为           .