The power of a point $(2,-1)$ with respect to a circle C of radius 4 is 9. The centre of the circle C lies on the line $x+y=0$ and in the $2^{\text {nd }}$ quadrant. If $(\alpha, \beta)$ is the centre of the circle C, then $\beta-\alpha=$

• A

  $-4$
• B

  $-10$
• Correct answer
  C

  $4$
• D

  $10$

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