Let m and M be the masses of the earth and the sun respectively and v the speed of the earth in circular orbit. To keep the earth in circular orbit, the gravitational force \\dfrac {GMm}{r^2} must balance the centripetal force \\dfrac {mv^2}{r} , i.e. \\dfrac {GMm}{r^2}=\\dfrac {mv^2}{r} or M=\\dfrac {v^2r}{G} Also, v=\\dfrac {2\\pi r}{T} . Using this, we get M=\\dfrac {4\\pi^2r^3}{T^2G} or M\\propto \\dfrac {r^3}{T^2} .Hence the correct choice is (c).