答:考试用B,平时随便.
在《Longman》词典中关于这一点就有如下说明:
Usage: Some people think a sentence such as "The reason for my absence was because I was ill" is bad English. It may be better to say: "The reason for my absence was that I was ill."
http://zhidao.baidu.com/question/494756271.html#answer-1240560756