A researcher plans to identify each participant in a certain medical experiment with a code consisting of either a single letter or a pair of distinct letters written in alphabetic order. What is the least number of letters that can be used if there are 12 participants, and each participant is to receive a different code?
A. 4
B. 5
C. 6
D. 7
E. 8
答案是B
不知道為什麼我怎麼算都只要四個數字就夠了
以1234四個數字推的話就有16種組合了
1 2 3 4 12 21 13 31 14 41 23 32 24 42 34 43
還是我搞錯題目的意思??
請幫我解答!!謝謝