be doing和be going to的区别和用法!

be doing和be going to的区别和用法! be going to do 和be doing用法的区别? be doing和be going to do的区别 be going to do和be doing的区别,急, be doing be is going to will用法的区别 be doing和doing的用法区别 be going to be,will be和be doing在用法上有什么区别,什么时候用什么 be going to do和be doing和want to do 三者之间的区别 is going to be 和 are going to be的用法区别 be doing 和will do 和be going to do 的区别 be used to do和be used to doing的用法和区别 be going to和be going to do的区别?