The earth is getting energy from the sun whose surface temperature is $$T_s$$ and radius is $$R$$. Let the radius of the earth be $$r$$ and the distance from the sun be $$d$$. Assume the earth and the sun both to behave as perfect black bodies and the earth is in thermal equilibrium at a constant temperature $$T_e$$. Therefore, the temperature $$T_s$$ of the sun is $$xT_e$$ where $$x$$ is

A

$$\sqrt{\frac{2d}{R}}$$

B

$$\sqrt{\frac{2R}{r}}$$

C

$$\sqrt{\frac{4d}{r}}$$

D

$$\frac{d}{R}$$