英语中当过去时一般现在时一般将来时同时存在时怎么表达

1.will常指没有经过计划临时出现的意图,常伴有说话人的主观意愿或将来必然发生的事.I will answer the door.我去开门
2.be going to 可表示主管打算做某事,也可表示客观上即将发生的事.
例如：They are going to set up a laboratory next year.
it's going to rain soon.
3.be to do 表示计划中约定的,按职责,义务要求必须去做的事或即将发 生的动作.
例：the Prime Minister is to visit China in May.
your assignment is to be handed in nest Monday.
4.be about to do表示眼下马上就要发生的,不强调主观,一般也不能与具体时状语连用.
例：Be quiet,the film is about to start.
Hurry up,the train is about to leave.