I must think of a proper gift for my mother, ________ won't be expensive but will make her happy.
A.who thatB.the one whichC.itD.one that在线课程D
该句意为“我一定要为母亲想出一个合适的礼物，一个不贵但能使她高兴的礼物”。此处选one相当于a gift，为泛指，不能选the one; that引导定语从句，修饰one。如选C项，应改为并列句…and it won't be…。