一般现在时，every day, usually , on Sundays 一般过去时， yesterday, last week, two days ago 一般将来时 tomorrow, next week, in two days 现在进行时，now , at the present, at the moment
过去进行时 at five yesterday evening, 现在完成时 for three year, since last week
过去完成时，by the end of last year 过去将来时 the next day,
这里列举的都是最基本的，具体题型中还有很多变化。
