常见八种时态标志词
1. 一般现在时 谓语用动词原形do或第三人称单数does形式。 标志词有: every day, every Sunday, often, always, usually, sometimes , on Sundays,in the morning, on weekdays,once a week等等
2. 现在进行时am/is /are doing形式。 标志词:now,at this time, at present,句首有Look!, Listen!Hurry!等警示语
3. 一般过去时用动词的过去式did 标志词有:yesterday, last week , last month, last year, 时间段 ago,two years ago，in 1979，the day before yesterday,just now=a moment ago刚才(与现在无关的明确过去时间)
4. 过去进行时:was/were doing 标志词:at that moment, at this time of yesterday, at eight last night,the whole afternoon.
5. 一般将来时用will do/be going to do. 标志词:tomorrow,tomorrow morning,in the future, next week , next Sunday,in 一段时间， soon=right=at once很快，立刻.
6. 过去将来时: would do 没有什么标志词，通常用在从句里。 I didn't know if he would come. .
7. 现在完成时 has/have done 标志词:already, yet,ever曾经,never从未,just刚刚(与现在有关的模糊过去时间),before，in the past 5 years, so far ,up to now, two times,for 时间段， since 时间点或从句 8. 过去完成时 had done 标志词:by/by the end of 过去时间，by the year 2010.... 如无标志词可根据句意，上下文，其他动词形式判断...
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