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答案：
A
6个人6个不
身高分别设为1,2,3,4,5,6。两排均需要满足从左到右递增，且第二排的必须比第一排高，可见第一排最左边必须是1，第二排最右边必须是6，否则无法满足题干条件。
接下来讨论其余四个数的排列：
当第一排第二个数是2时，第一排第三个数在其余三个数中选择一个即可，选完后剩下的两个数按照大小顺序排在第二排剩余位置时只有一种情况。因此第一排第二个数是2时有3中排法。
同理，当第一排第二个数是3时，第一排最后一个数只能在4、5中二选一，选完后剩下的一个和2按照大小排在第二排。第一排第二个数是3时有两种排法。
而当第一排第二个数是4时，第一排第三个数和第二排第二个数都需要比4大，此时只有5比4大，排法不成立。同理，第一排第二个数也不可能是5。
综上所述，总计有3+2=5种排法，分别是：
4,5,6 3,5,6 3,4,6 2,5,6 2,4,6
1,2,3 1,2,4 1,2,5 1,3,4 1,3,5 
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