For a planet moving aroung the sun in an elliptical orbit, which of the following quantities remain constant?

Question

1) Total energy of the sun-planet system

2) The angular momentum of the planet about the sum

3) The force of attraction between the two

4) Linear momentum of the planet

$\begin{array}{1 1}(a)\;1,2\\(b)\;3,4\\(c)\;1,2,3\\(d)\;1,4\end{array}$