A circular tube of mean radius `8 cm` and thickness `0.04 cm` is melted up and recast into a solid rod of the same length. The ratio of the torsional rigidities of the circular tube and the solid rod i

Options

A. `((8.02)^(4)-(7.98)^(4))/(0.8)^(4)`
B. `((8.02)^(2)-(7.98)^(2))/(0.8)^(2)`
C. `((8.02)^(2)-(7.98)^(2))/(0.8)^(2)`
D. `(0.8^(2))/(8.02^(3)-(7.98)^(2)`