不一定.形容词性物主代词放在句中是对的,因为必须加名词.但是名词性物主代词也可以在句子中间.例如 Your book is on the desk,mine is in my schoool bag.形容词性物主代词后面必须加名词，例如 my pen your name名词性物主代词后面不加名词例如 This is hers。Yours is better.