it is a cat 怎样改为复数形式?

it is a cat 怎样改为复数形式? This is a cat.(改为复数形式) It is a dictionary改为复数形式 It is a watch.(改为复数形式) is it a bus改为复数形式 It is a photo.(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) There is a nice cat in the tree.改为复数形式 Is it a cat?要求变复数 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 is it a desk?（改为复数形式） it is a box.(改为复数形式）帮忙啊! 英语句的复数形式What is this?It is a desk.改为复数形式 What is it 改为复数形式 Here it is.改为复数形式 It is my pen.(改为复数形式) whose coat is it?改为复数形式, it is a cat(用a tiger改为选择疑问句）she has a nice photo.(改为复数）求救