Three circle $$C_1, C_2$$ and $$C_3$$ with radii $$r_1, r_2$$ and $$r_3$$ (where $$r_1 < r_2 < r_3$$) are placed as shown in the given figure. What is the value of $$r_2$$?

A

$$\surd(r_1r_3)$$

B

$$\frac{(r_1 + r_3)}{2}$$

C

$$\frac{(2r_1r_2)}{(r_1 + r_2)}$$

D

$$\surd(r_1 + r_3)$$