题目是这样的
If a code word is defined to be a sequence of different letters chosen from the 10 letters A,B,C,D,E,F,G,H,I,J, what is the ratio of the number of 5-letter code words to the number of 4-letter code words
A 5 to 4
B3 to 2
C2 to 1
D5 to1
E6 to 1
答案是E
我连题目都不知道在说什么 | 
