you know……?

题目

you know……?
A.when they have a discussion about B.How didi they arrive there
C.what we will do next D.If he is a doctor or not
答案貌似是C.D为什么不可以?

答案

D中的if要换成whether就可以了.因为后面有or not ,所以只能用whether,不能用if.