be about to +动词原形，意为马上做某事，不能与tomorrow，next week 等表示明确将来时的时间状语连用。
be about to +动词原形，意为马上做某事，不能与tomorrow，next week 等表示明确将来时的时间状语连用。
be going to ,will
用于条件句时，be going to 表将来
will 表意愿
be to 和 be going to
be to 表示客观安排或受人指示而做某事，be going to 表示主观的打算或计划
一般现在时表将来
1.时间状语从句，条件句中，从句用一般现在时代替将来时When, while, before, after, till, once, as soon as, so long as, by the time, if, in case (that), unless, even if, whether, the moment, the minute, the day, the year,immediately
