Speed of a planet in an elliptical orbit with semi major axis 'a' about sum of mass M at a distance r from the sun is

Question

\[(a)\;\sqrt {GM \bigg(\frac{2}{r}-\frac{1}{a}\bigg)} \quad (b)\;\sqrt {GM \bigg(\frac{1}{r}-\frac{1}{a}\bigg)} \quad (c)\;\sqrt {GM \bigg(\frac{1}{r}-\frac{2}{a}\bigg)} \quad (d)\;\sqrt {\frac{GMr}{2a^2}} \]