Question

We don’t know ______ it next. Let’s go and ask Mr Li.
A what to do   B to do what    C whether to do    D to do whether

Answer 1

C

动词不定式作定语时要放在所修饰词的后面，whether to do是如何去做的意思，what to do是做什么的意思。It是我们做的对象，我们应是不知道是否去做，所以选C.