I want to buy a gift,____ is expensive为什么这道题不能填which呢?老师说要填one which,one做同位语,which不是主句中的一个词或整体内容都能代替吗?

I want to buy a gift I want buy a gift 哪个对?为什么 I want to buy my mother a gift 英语 连词成句（my,gift,I,to,to,buy,mother,a,for,want) tomorrow is Mary's birthday i want to buy a gift for___(her） I want to buy a gift for my mother 用一般过去式改写句子 连词成句.my,gift,I,to,buy,mother,a,for,want. I made some money to buy him a gift.请问这里为什么要用to buy I want to a gift,my birthday is coming I want to buy a house _______money. I want to buy a present______mu cousin I want to buy a hair c____ I+want+to+buy+a+postcard. I want to buy a _______of shorts. I want to buy a p____of shose want,ruler,buy,I,a,to I want to give her a gift与 get her a gift有区别吗 I want to buy a gift ______(to/for) my mother .是填()还是填()说明原因六年级上册书上有两个句子:1 Then LiMing gives his gift to Mr.andMrs.Smith.2 This is for everyone. I want to buy a pair of_shoes I want to buy a paiI want to buy a pair of_shoesI want to buy a pair of_shoes