Consider a closed surface S surrounding a volume V. If \[\overrightarrow r \] is the position vector of a point inside S, with \[{\hat n}\] the unit normal on s, the value of the integral \[\mathop{{\int\!\!\!\!\!\int}\mkern-21mu \bigcirc}\limits_S {5\overrightarrow r .\hat ndS} \]   is

A. 3 V

B. 5 V

C. 10 V

D. 15 V

Answer: Option D