Yes please.
Sure thing! This kinda is hard to understand, so I'll see if I can explain it properly
We know that acceleration = F/m
and that gravitational force is GmM/d^2
but as we have now defined force as F/m, we must also divide the gravitational force by m (the mass of the object)
So since we have defined acceleration as the objects force over their respective masses (the inversely proportional part of the answer!!)
And that force equalling the gravitational force, but without their respective masses. We here have explained how answer D is correct!
This is kinda tough to get your head around (and hence why I said this is best answered by removing the wrong answers) but I hope this makes sense.
If it didn't I'll happy to elaborate the confusion