by the time of last term ,we have finish all the lessonswe had invented many new things by the time of last years两个句子都是by the time ,主句的时态为什么不同?

by the time of last term ,we have finish all the lessonswe had invented many new things by the time of last years两个句子都是by the time ,主句的时态为什么不同?
by the time of last term ,we have finish all the lessons
we had invented many new things by the time of last years
两个句子都是by the time ,主句的时态为什么不同?

by the time of last term ,we have finish all the lessonswe had invented many new things by the time of last years两个句子都是by the time ,主句的时态为什么不同?
第一个句子【by the time of last term ,we have finish all the lessons】错误,正确的表达是：
By the time of last term ,we had finished all the lessons.
by the time of 表示“到...的时候”,句意是：在上个学期为止,我们已经学完了所有的课程.这里需要用过去完成时态,其结构是：had + 过去分词.过去完成时指：某一动作在过去某个时间或者动作之前发生,即发生的时间是“过去的过去”.有关过去完成时的定义、用法请参考：http://baike.baidu.com/view/201153.htm
第二个句子【we had invented many new things by the time of last years】,其实,也有一点小错误.正确的是：We had invented many new things by the time of last year.
这里的years不需加S.具体的解析请参考上面的.

第一句话错了,改为by the time of last term , we had finished all the lessons.
第二句话正确的

不但是时态不同的问题，是两个句子写错了：
第一个句子不能说：by the time of last term , we have finish all the lessons，应该是：By the time the term was over we had finished all the lessons （assessment of a past event，过去式）
或 By ...

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不但是时态不同的问题，是两个句子写错了：
第一个句子不能说：by the time of last term , we have finish all the lessons，应该是：By the time the term was over we had finished all the lessons （assessment of a past event，过去式）
或 By the time the term is over we will have finished all the lessons. （prediction of a future event，未来式）
第二个句子：We had invented many new things by the time of last years，写错了，没有by the time of last years 这样的说法，只有 by the time of last year's + 名词，比如：by the time of last year's Christmas，应该是：We (had) invented many new things by the time of last year's second half/Christmas/New year's eve
此外只能用 during/in the last few years: We had invented many new things in the last few years. （过去式）
We will invent many new things by the time the year is through/over. （未来式）
类似的例子：
By the time the term was over in April the snow had (already) melted.（过去式）
By the time the term is over in April the snow has melted.（narrative未来式）
What if I hadn't finished my hours by the time the term was over? （过去式）
What if I do not finish my hours by the time the term is over? （未来式）

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