23, 2, 21, 6, 19, 12, 17, ( )A.18 B.20 C. 发布时间:2018-01-05 00:58 │ 来源:www.tikuol.com 题型:单项选择题 问题: 23, 2, 21, 6, 19, 12, 17, ( )A.18B.20C.15D.13