We must be careful_____(cross) the road.

We must be careful_____(cross) the road.
We must be careful_____(cross) the road.

We must be careful_____(cross) the road.
crossing 状语

to cross
望采纳，谢谢

We must be careful_to cross____(cross) the road.
be careful to do sth 小心去做某事

crossing
过马路是我们必须小心。

crossing