sister是不是可数名词

　　She's never really got on with her sister.

　　她从未与妹妹真正和睦相处过。

　　I'm going around to my sister's later.

　　我打算不久后到姐姐家去看看。

　　We have our differences, but she's still my sister.

　　我们之间虽然不和，但她仍旧是我的妹妹。

　　Her sister is a big girl, isn't she?

　　她姐姐是个大个子胖姑娘，是吗？