Two air bubbles with radii $$r_1$$ and $$r_2$$ $$(r_2 > r_1)$$ formed of the same liquid stick to each other to form a common interface. Therefore, the radius of curvature of the common surface is

A

$$\sqrt{r_1 r_2}$$

B

infinity

C

$$\frac{r_2}{r_1}\sqrt{r_2^2 - r_1^2}$$

D

$$\frac{r_1 r_2}{r_2 - r_1}$$