1/3,1/7,1/13,1/21,( ) A.1/28 B.1/29 C.1/3 发布时间:2017-02-26 11:20 │ 来源:www.tikuol.com 题型:单项选择题 问题: 1/3,1/7,1/13,1/21,( )A.1/28B.1/29C.1/30D.1/31