————,it is dangerous to look out of windows when are on the train.

问题描述:

————,it is dangerous to look out of windows when are on the train.
有3个选项
A.Look up B.Look out C.Look after

选B
因为look up有查询,抬头看等意思,可以说look up the dictionary
而look after 是照顾照料的意思,look after the child
look out 有当心,小心的意思,所以选、B