by the end of和at the end of区别

By the end of的意思是:到…为止 。通常跟完成时连用。例如you should finish the work by the end of this year，你应该在年底前完成这个任务。或者说they had finished their task by the end of last year，他们在去年年底前已经完成了任务。

at the end of的意思是:在…末端尽头。比如you will get the money at the end of the year，你会在年底的时候得到这笔钱。