Let $X=\{1,2,3, \ldots, 25\}$. If a student selects a function randomly from the set of all functions from $X$ onto $X$, then what is the probability that the selected function maps prime numbers to prime numbers?

• A

  $\frac{9!}{25!}$
• B

  $\frac{16!}{25!}$
• Correct answer
  C

  $1 /\binom{25}{9}$
• D

  $9!/\binom{25}{9}$

Hence, the correct answer is option: 'C'.