I will be back 和I will back.为什么要加be?

问题描述:

I will be back 和I will back.为什么要加be?
I wil be with you .with 呢

要加,back 是副词,不是动词.系表结构,要有个系动词beI wil be with you . with 呢此句be 和with 都不能缺。