by和before用法有什么不同

by是截止到什么时间
before是....时间以前
差不多的
反对上楼的
by可以用在一般现在时
英语课本上就有原句
before也可以用在过去时态，过去完成时...

by 在句子中时主句要用完成时。

用befoer时，主句一般为一般时。

BY
作介词prep.

1. 被,由
The homework was assigned by the teacher.
这些家庭作业是老师布置的。

2. 靠,用,通过
They crossed the river by ferry.
他们乘渡船过了河。

3. 经由;沿
Ellen flew to Chicago by way of Minneapolis.
艾伦经由明尼阿波利斯飞往芝加哥。

4. 在...旁边,靠近;在...手边
I haven't got any money by me.
我身边没有带钱。

5. 不迟于;在...之前
We had to get there by evening.
我们必须在夜晚前抵达那里。

6. 根据,按照
How do you know he didn't act by the rules?
你怎么知道他没有按规定行事?

7. (表程度)相差
He missed the bus by three minutes.
他晚了三分钟没赶上那班公车。

8. 凭,对...(发誓)
I swear by God!
我对上帝发誓!

9. (乘除法上)以...,用...(乘或除)
Nine divided by three makes three.
九除以三得三。

10. 以...计,按
You'll be paid by the hour.
你