1.一般过去时:last year(month,week,century),yesterday,in 1988,3 years ago...
2.现在完成时态:since 1999,since 3 years ago,for two months,for 3 hours...,yet,ever,never...;
3.现在进行时:now,at the moment;
4.将来时:in 2010,in the future,in two years,in three weeks...;
5.一般现在时:常用的频度副词always,usually,often,sometimes,seldom,never等;
6.将来完成时:by the end of + 将来时间,by + 将来时间;
7.过去完成时:by the end of + 过去时间;
8..