答案：B

题目分析：句意：——你将要去做什么？——我将要去拜访我的叔叔。A.Why are you going to visit your uncle   你为什么要去拜访你的叔叔？B.What are you going to do 你将要去做什么？C.Are you going to visit your uncle  你将要去拜访你的叔叔？   D.How are you going to visit your uncle你将如何去拜访你的叔叔？

根据I am going to visit my uncle可知对方问的是他要去做什么？故选B。