什么时候主语后面接BE动词,什么时候不用?

be动词的用法 be [bi:] vi 现在时 I am,you are,he is,we are,you are,they are （缩略式 I'm,you're,he's,we're,you're,they're）,（否定缩略式 I'm not,isn't,aren't）,过去时 I was,you were,he was,we were,you ...