How beautiful these ( )(雨衣)are I want to buy one

how much are these 【 i want to buy a kilo These _____(watch) are very nice.I want to buy one. These three books are good for me,I want to buy them____(全部) Mom,my shoes are too old,I want to buy a new____ A.one B.one I want to buy a pair of shoes.-------How about this A.one B. I like these books,I want to buy( )扩号里填什么? My trainers are very old,I want to buy a new one.改错 Two pens are lost,I want to buy a t_____ one Both oftwo rulers are broken. I want to buy a( )one. A.three where are the ______ in your shop I want to buy one .a dress where are the ______ in your shop I want to buy one . i want to buy ones和i want to buy one的区别是什么?