Question

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？

Answer 1

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.
解释：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.
解释：这里的years不需加S。具体的解析请参考上面的。

祝你学习进步，更上一层楼！请记得采纳，谢谢！(*^__^*)

Answer 2

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）

Answer 3

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