The cross-section of a road partly in banking and partly in cutting is shown in the given figure. The area of the shaded portion is

A. $$\frac{1}{3} \times \frac{{{{\left( {{\text{b}} - {\text{rd}}} \right)}^2}}}{{{\text{r}} - {\text{s}}}}$$

B. $$\frac{1}{3} \times \frac{{{{\left( {{\text{b}} - {\text{rd}}} \right)}^2}}}{{{\text{r}} + {\text{s}}}}$$

C. $$\frac{1}{2} \times \frac{{{{\left( {{\text{b}} + {\text{rd}}} \right)}^2}}}{{{\text{r}} - {\text{s}}}}$$

D. $$\frac{1}{3} \times \frac{{{{\left( {{\text{b}} - {\text{rd}}} \right)}^2}}}{{{\text{s}} - {\text{r}}}}$$

Answer: Option A