An equilateral triangle ABC is inscribed in a circle as shown in figure. A square of largest possible area is made inside this triangle as shown. Another circle made inscribing the square. What is the ratio of area of large circle and the small circle?

A

$$(15 - 12\surd3) : 1$$

B

$$(63- 36\surd3) : 4$$

C

$$(7 - 4\surd3) : 8$$

D

$$(18 - \surd3) : 2$$