Technically - none of them (but they are looking for D as the answer) cos "gravity" is not a "force" - its an effect caused by the distortion of space/time itself It is NOT a "force" caused by the earth attracting the moon, or the sun attracting the earth (the equation identified by "electron" technically is not correct either cos the equation implies that if either M or m become zero then Fg immediately becomes zero i. E if "M" were to suddenly become zero then its effect on "m" would happen immediately (i. E if M = the sun were to disappear then the m = the earth would fly off in the direction it was going when the sun disappeared ) this is NOT the case - cos einstein proved this effect cannot travel faster than light THEREFORE "M" becoming zero would take time to have an effect on "m" I.
E if M= the sun were to disappear then the earth would not feel any effect until the effect of the change in mass of the sun got from where the sun was to the earth, THAT travels at the speed of light and it takes 8.5 minutes for light to get from sun to earth THEREFORE the earth would continue in orbit around the sun for a further 8.5 minutes after it had disappeared even though the sun would not be there for those 8.5 minutes THEREFORE the equation MUST be wrong) (its a shame science teaching persists in teaching newton's version of gravity when it was proved wrong 100 years ago).
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.