网络歌手光光真的死了吗?具体是什么时间?

解题思路：分情况讨论，甲、乙同去，则丙不去；甲、乙同不去，丙去；甲、乙、丙都不去，根据分类计数原理得到结果．

分两步，
第一步，先选四名老师，又分两类
第一类，甲去，则乙一定去，丙一定不去，有C₅²=10种不同选法
第二类，甲不去，则乙一定不去，丙可能去也可能不去，有C₆⁴=15种不同选法
∴不同的选法有10+15=25种
第二步，4名网络歌手同时去4个地区演出，有A₄⁴=24
最后，两步方法数相乘，得25×24=600
故选D．

点评：
本题考点： 排列、组合及简单计数问题．

考点点评： 本题考查了排列组合的综合应用，考查分步计数原理的运用，考查学生的计算能力，属于中档题．

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