一道数学题

kuuiytt

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, and 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

B. 3 to 2

C. 2 to 1

D. 5 to 1

E. 6 to 1

这到题的解题思路是什么啊 ，怎么不是A啊

jojofgasw

P5,5/p4,4====5:1.