I don't know when__back to Beijing.When__,I'll call you.

问题描述:

I don't know when__back to Beijing.When__,I'll call you.
A.going;arriving B.to ;go C.going ;to arrive D.to go ;to arriving

D.你是否把答案写错了
前面是宾语.后面是时间状语.应该是 to go / arriving