Consider the circles $x^2+y^2+2 a x+c=0$ and $x^2+y^2+2 b y+c=0$. What is the distance between the centres of the two circles?

• Correct answer
  A

  $\sqrt{a^2+b^2}$
• B

  $a^2+b^2$
• C

  $a+b$
• D

  $2(a+b)$

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