by the end of ...是在什么结束之前的意思
一般是跟完成时态连用的,举例说吧:I will have finished my homework by the end of the week.
at the end of ...在什么的终点或者在什么结束的地方,强调的是点
at the end of the road
at the end of the week
We'll have an exam in English at the end of January.
一月底我们要参加英语考试。
选A
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