In the diagram given below, there are three lenses formed. Considering negligible thickness of each of them as compared to $$\mid R_1 \mid \text{ and } \mid R_2 \mid$$, i.e., the radii of curvature for upper and lower surfaces of the glass lens, the power of the combination is

A

$$\frac{1}{6}\left(\frac{1}{\mid R_1 \mid}-\frac{1}{\mid R_2 \mid} \right)$$

B

$$-\frac{1}{6}\left(\frac{1}{\mid R_1 \mid}+\frac{1}{\mid R_2 \mid} \right)$$

C

$$\frac{1}{6}\left(\frac{1}{\mid R_1 \mid}+\frac{1}{\mid R_2 \mid} \right)$$

D

$$-\frac{1}{6}\left(\frac{1}{\mid R_1 \mid}-\frac{1}{\mid R_2 \mid} \right)$$