This is a cat.(改为复数形式)

This is a cat.(改为复数形式) This is my book.(改为复数形式) There is a nice cat in the tree.(改为复数形式)Those are rulers.(改为单数形式) This is my book.改为复数形式 There is a nice cat in the tree.改为复数形式 Those are rulers 单数形式 it is a cat 怎样改为复数形式? this is a beautiful cat 改成复数形式 This is a book 改为复数句 This is a pear.改为复数句 this is a book改为复数形式 This is a dress.改为复数形式 this is a tree 改为复数句 Is this a bus （改为复数句 This is a bus.改为复数. this is a shirt改为复数句 this is a strawberry改为复数 This is a young tree.(改为复数) this is a watch(改为复数句) This is a knife 改为复数 this is a pen.改为复数句