Two asteroids, each with mass M$,$ are floating in space a distance R away from each other and experiencing a mutual gravitational force of F$.$ What is the new strength of the force if$...$

A$)$ The distance between them becomes $2$R$?$

B$)$ The distance between them becomes $1/3$ R

C$)$ The mass of one planet becomes $4$M$?$

D$)$ The mass of both planets becomes $3$M$,$ and the distance becomes $1/2$ R$?$