英语中be用单数还是用复数由谁来决定?

由主语决定，当然有特殊情况，如There is a desk and some chairs in the room.这时be动词由靠近be的主语决定。

be 成为系动词，单数复数由它的主语（动作发出者，即什么、谁） 来决定

I am a student. -- am
I was a student ten years ago. -- was
He is a doctor. - is
He was a doctor when he was 30 years old. -- was
They are friends. -- are
They were enimies. -- were
This glass is broken. -- is
The magazines were published years ago. -- were

作为谓语的动词,以及be动词永远都是由主语来决定的!当然还要分辨时态!

主语