The correct expression for finding the period of a planet revolving around the Sun is

The time period of a planet(T) is related with the radius of the orbit(r) as,
[tex]T^2=\frac{4\pi^2r^3}{GM_s}[/tex][tex]M_s\text{ is the mass of the Sun}[/tex]G is the gravitational constant.
hence, option C means the 3rd option is correct.