Question

whose is this book 错在哪，为什么

Answer 1

没错 都可以---whose is it?这里相当于把it换成 this book

Whose is that computer?那台电脑是谁的?（作表语）Whose sweaters are these?这些是谁的毛衣?（作定语）whose用来对物主代词及名词所有格进行提问：
1．提问形容词性的物主代词.如：These are my bananas.→Whose bananas are these?
2．提问名词性的物主代词.如：That bedroom is mine.→Whose is that bedroom?Hers are in the classroom.→ Whose are in the classroom?
3．提问名词所有格（不包括of构成的所有格）.如：Those are the twins’ bags.→ Whose bags are those?Tom’s mother is a good teacher.→ Whose mother is a good teacher
4.Whose 可针对my,your,our,their,Kate’s等形容词性物主代词提问,其语序为：
These are their sweaters.这些是他们的运动衫.
Whose sweaters are these?这些是谁的运动衫?

（针对定语提问）
whose 也可针对mine,yours,ours,theirs,Kate’s等名词性物主代词或名词所有格提问.
This shirt is his.这件衬衫是他的.
Whose is this shirt?这件衬衫是谁的?

（针对表语提问）
对画线部分提问
Those are her trousers.
Whose trousers are those?（提问表语的定语）
That cup is mine.
Whose is that cup?（提问表语）

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Answer 2

whose is this book是错的，你看whose是谁的的意思，is是是的意思，this是这的意思，book是书的意思，无论如何翻译都是不通顺的，应该改为： whose book is it?
有时候翻译器的翻译只是根据字面或近似词翻译，不一定是对的

Answer 3

Whose book is this?