In the given circuit if the power rating of Zener diode is $$10$$ mW, the value of series resistance $$R_s$$ to regulate the input unregulated supply is: 

A

$$\frac{3}{7}$$ k$$\Omega$$

B

$$10\ \Omega$$

C

$$1$$ k$$\Omega$$

D

$$10$$ k$$\Omega$$