be about to do表"立即的将来"。如：The train is about to start.火车马上就要开了。be to表按计划或安排要做的事。但不表示“立即”。如：She is to get married next month. 她下个月结婚。
be about to do表"立即的将来"。be to表按计划或安排要做的事。
