What do you do when you meet an old man ____ the world?

问题描述:

What do you do when you meet an old man ____ the world?
A.cross
B.to cross
C.crossing
D.crosses

C
when you meet an old man ____ the world里,已经有了一个谓语动词meet,第二个动词cross就要变成非谓语,bc就是非谓语动词,但是不定式表将来,crossing表伴随状态,做定语,修饰old man
所以选C