If $m$ and $\mathrm{M}$ are respectively the smallest and greatest rational roots of the equation $6 x^6-25 x^5+31 x^4-31 x^2+25 x-6=0$, then $\mathrm{M}-m=$

• A

  1
• B

  2
• Correct answer
  C

  3
• D

  4

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