过去现在将来一般did was/were标志词：1)yesterday morning(afternoon, evening)等；2)last night/year等；3)时间段+ago；4)介词+一时间名词（例如：on Friday）5)then, just now, once,以及由after或before构成的介词短语do/does is/am/are标志词：1)often、 usually、always、 sometimes、 every day、once a week等频度副词，2)on Saturdays、 in the morning (afternoon, evening) 等be going to do/will do标志词：tomorrow，next week/month/ year 等进行was/were doing标志词：1)at that moment, at ten oclock last night ,(at) this time of l
