大家知道,表时间的by短语常常与过去完成时连用。如By 1555 corn had already become important here.有时还常与将来完成时连用。如By the end of next term we will have learned 3,000 words.

　　但在实际运用时,与by短语连用的时态远远超出了上面所提到的常规时态的使用范围,现分述如下。

　　一、若谓语动词是状态动词,则谓语动词可用一般过去时、一般现在时或一般将来时。例如:

　　By then he knew what he wanted to be when he grew up.

　　到那时他已明白长大后要干什么。

　　By now we each have a home-made computer.

　　现在我们每人有一台国产电脑。

　　Your son will be all right by sup-per time.

　　到吃晚餐时,你儿子会好的。

　　但谓语动词有"for+时间段"来强调状态持续了多长时间时,则谓语应用过去完成时或将来完成时。例如:

　　By yesterday evening he had been waiting for three days.

　　到昨晚为止,他等了三天了。

　　By then he will have been in Canada for seven years.

　　那时他将在加拿大呆有七个年头了。

　　二、有时谓语动词以"情态动词(must, have to, can, may等)+动词原形"的形式出现,表示现在或未来的状态或动作。例如:

　　He must be in Beijing by this time.到此时他一定在北京。

　　We can be ready by Saturday.到星期六我们能准备好。

　　Can you finish the work by Friday?到星期五你能完成这项工作吗?

　　The train leaves at 6:00 am. So I have to be at the station by 5:40 am at the latest.(NMET'97)

　　火车早上6点走,我得最迟5:40到车站。

　　三、有时谓语动词用过去进行时或现在进行时。例如:

　　By the time we got to the third floor, my Dad was still complaining.我们到达三楼时,父亲还在抱怨。

　　By seven o'clock, the wind was blowing harder than ever.

　　到七点钟时,风刮得比以前更猛了。

　　By now, all the students are preparing hard for the college entrance examination.

　　现在所有的学生都在为高考做准备。

　　四、有时可用于祈使句中。例如:

　　Hand in your papers by the time class is over.

　　下课时,必须把试卷交上来。

　　Please come here by this time tomorrow.

　　请在明天这个时候到这里来。

　　China Makes More Effort To Protect Hiritage

　　(文/湖南岳巧玲；英语通高中一年级版2003年第10期；版权归英语辅导报社所有，独家网络合作伙伴新浪教育，未经许可，不得以任何形式进行转载。)