When two soap bubbles of radii $$a$$ and $$b$$ ($$b > a$$) coalesce, the radius of curvature of common surface is:

A

$$\frac{ab}{b-a}$$

B

$$\frac{a+b}{ab}$$

C

$$\frac{b-a}{ab}$$

D

$$\frac{ab}{a+b}$$