I did not buy a new notebook____my mother gave me one

题目

I did not buy a new notebook____my mother gave me one
a.if b.because c.until d.before

答案

b,我没有买新笔记本,因为我妈妈给了我一个,
此句都是发生在过去的,所以都用过去式,because 表示原因,可以用在这里.