he isn"t my borther but my friend 因为这是连接表语成份.and /but/ or 接表语成份时,就可以省略很多.Is it an apple or banana?That is good and sound .they weren"t fighting each other but were playing toget...并列句可以省主语 还可以省什么？连接表语成份 还可以省什么？