过去的动作,如果句子里有过去时间状语,如,in 1988, three years ago, last week, yesterday就要用过去时态。 --He came to Shanghai in 2006. --He came to Shanghai three years ago. 过去的动作,句子里没有这类时间状语,就要用现在完成时。如, --He has been to Beijing for three years. --He has lived here since 2006. 总之,就是过去的动作,对现在有影响;或者,过去的动作,到现在仍然在延续,就要用现在完成时。 其他的例子, 自己体会: --Close the window in that room now. --I have closed it. (现在完成时) --When did you do it? (过去时) --I closed it half an hour ago. (过去时)