__________of this month,we will finish planting all the treesat the end?by the end?

__________of this month,we will finish planting all the treesat the end?by the end?
__________of this month,we will finish planting all the trees
at the end?by the end?

__________of this month,we will finish planting all the treesat the end?by the end?
By the end
by the end of this month,是指到这个月末为止,用于将来时,表示经过一段时间.而at the end of this month是指在这个月末,是点时间.

by the end
因为后面是将来完成时，故by表示“在...时间之前、不迟于...” ；而At却表示“在...时间”

by the end of 是“到......末”的意思，后边跟不同的时间会有不同的含义和用法。
A 跟将来的时间，就用一般将来时，如
By the end of next month，I will finish reading this book.(到下个月末，我将读完这本书）。

By the end
at the end：到最后、最终的时候，一般与过去时连用
by the end of ..：到..时候为止、截止，一般与将来时或完成时连用