如何回答 Whose is this

如何回答 Whose is this Whose guitar is this?类似于这种的疑问句怎么回答? whose is this book? Whose book is this? Whose hat is this? “Whose room is this? whose shirt is this ---Whose dress is this? --whose watch is this ?---【 】,回答为什么不能是this is lucy‘s 而是it is This is our classroom.（一般疑问句,肯定回答） Whose book is this?（复数句） whose is this bag?和 whose bag is this? 看这两句有啥区别?whose is this shirt? whose shirt is this?