初中英语 they weren"t fight each other but were playing together at this time yesterday 中

题目

初中英语 they weren"t fight each other but were playing together at this time yesterday 中
为什么有but were 为什么有were呢
he isn"t my borther but my friend中 就不是he isn"t my borther but is my friend呀 but什么时候要加be动词 什么时候不用加阿

答案