If the roots of the equation $x^2-4 x-\log _3 \mathrm{~N}=0$ are real, then what is the minimum value of N ?

• A

  $1 / 256$
• B

  $1 / 27$
• C

  $1 / 64$
• Correct answer
  D

  $1 / 81$

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