y经常是与完成时联系在一起,具体什么完成时取决于by之后的时间,例如by 2013是过去完成时,by now是现在完成时,by 2015是将来完成时
by＋时间”与动作性强的动词连用时,主句多用于完成式.by 后的时间可指现在、 过去或将来时间点.如：By the time he was fourteen years old,he had learned maths all by himself.到14岁的时候,他就已经自学了数学[SB 2B p.2].I shall have finished it by the time you come back.你回来以前我就把它做完了[1].By the end of the match,they had kicked two goals and we had kicked four.[JB p91] 比赛结束时,他们踢进了2分我们踢了4分.They must have finished their work by this time.他们现在一定已经完成工作了[2].但是,上述情况中当时间为将来时,主句动作发生在从句动作之后时,主句动词可用一般时态.如：If you're not better by then,I'll take you to see the doctor.[JB3 p.85] 如果到那时还不好些,我就带你去看病.Can you finish this by tomorrow?在明天以前你能做完这件事吗[1]?间或有用进行式的.如：By the end of the first week the head of the department was saying very nice things about me.第一周末时系主任给我多多美言了几句 [3].
