nOone knows----how the robbery happened in this store last night.Maybe someone broke into the the store and robbed the v
问题描述：
nOone knows----how the robbery happened in this store last night.Maybe someone broke into the the store and robbed the valuble watches.
A.to be sureB.make sure C.for sure 为什么?
答
（A）和 （B）都有动词,所以不能接上前面的动词"knows",只有(C)作为状语时才能接得上