英语语法，时态问题，如图，为什么要用完成时？

Question

如题所述

Answer 1

将来完成时，表示到明年这个时间点时，攒钱这个动作已经完成了。攒钱的动作发生在限定时间点之前，因此使用完成时。

Answer 2

这是将来完成时追答

表示到明年他可能已经凑够钱了

Answer 3

by the time和by that time均与完成时相连用，可能是现在完成时，过去完成时或将来完成时。by这个介系词加一个时间，也可以与完成时相连用，区别如下：
by the time具有从属连接词的特征，称为短语连接词，后面可以接一个完整的句子，是时间状语从句，这个时间状语从句的主句用完成时。如：
By the time he's twenty, he'll know everyone worth knowing
in Washington.
到20岁时，他就会认识华盛顿所有值得认识的人。
The storms had abated by the time they rounded Cape Horn.
他们绕过合恩角时，暴风雨已经减弱。
By the time we had to sell, prices had fallen catastrophically.
等到我们不得不出手的时候，价格已经崩盘了。
She had slipped into a coma by the time she reached hospital.
到医院时，她已陷入昏迷。
by that time是单独作为时间状语使用的，后面不能接句子。如：
By that time the steel output will have greatly increased.
到那会儿钢的产量将大大增加。
By that time her enthusiasm had cooled.
到那时她的热情已经冷却了下来。
The enemy's arsenal had been uncovered by that time.
敌人的军火库那时已暴露了。
By that time they should have fetched up in Qingdao.
到那时候他们应该已经抵达青岛了。
希望我能帮助你解疑释惑。本回答被网友采纳