试题在这:http://wenku.baidu.com/view/baa405d4b14e852458fb5773.html
1 2 3 4 5 6 7 8 9 10
B A C D A B B C D A
11 12 13 14 15 16 17 18 19 20
C D D D B D D A C B
21 22 23 24 25 26 27 28 29 30
A C A D B A C D A D
31 32 33 34 35 36 37 38 39 40
D A C A C B D D D C
41 42 43 44 45 46 47 48 49 50
D C D D B A B B B A
51 52 53 54 55 56 57 58 59 60
AD CD AC AB CD AD AB AC CD BD