be to do和be about to do有什么区别?

题目

be to do和be about to do有什么区别?

答案

两者区别在于:
be to do:有责任,义务,约定的含义.
e.g Parents are to take care of their children.
be about to do:表即将做某事．
e.g The plane is about to take off.