"这是我的书" This is my book = This book is mine。孩子写 This is mine book，就错了。
物主代词分两派，差别就一个：后面要不要再放名词。
形容词性：后面必须跟名词
my、your、his、her、its、our、their 这七个，相当于形容词，后面必须接名词：
- This is my book.
- Her dog is cute.
名词性：自己就是名词，后面不接东西
mine、yours、his、hers、its、ours、theirs 这一组，已经包含"东西"在里头，后面不能再放名词：
- This book is mine.（= my book）
- The choice is yours.（= your choice）
一张表对照
- my → mine
- your → yours
- his → his（一样）
- her → hers
- its → its（一样）
- our → ours
- their → theirs
its 和 it's 是两回事
- its = 它的：The dog wagged its tail.
- it's = it is / it has：It's a dog.
一句话：后面有名用形容词性，后面没名用名词性，his 和 its 两派长得一样别慌。
