When only the force of gravity dose work on a system, the total mechanical energy of that system is conserved : true or false ?

Ibelieve the answer is b

Answer (d) the universe had cooled enough for atoms to combine, protons and neutrons were too far apart to form nuclei;

We can infer that star y is closer but other factors must be considered including the heat of the star, the mass, and the brightness of the star. even though star x seems dimmer it may just be less bright or contain less heat.

It would stay the same