I don’t know _______ they have passed the exam.这里答案是if/whether,但是我觉得when跟how填进去也说得通啊.请问为什么不能填when跟how、?

问题描述:

I don’t know _______ they have passed the exam.
这里答案是if/whether,但是我觉得when跟how填进去也说得通啊.请问为什么不能填when跟how、?