Answer:
D. half as much
Step-by-step explanation:
let m and M be the mass of the planets and r be the distance between them.
then: the force of attraction between them is given by,
F = G×m×M/(r^2)
if we keep one mass constant and double the other and also double the distance between them.
the force of attraction becomes:
F1 = 2G×m×M/[(2×r)^2]
= 2G×m×M/[4×(r)^2]
= (1/2)G×m×M/(r^2)
= 1/2×F
therefore, when you double one mass and keep the other mass constant and double the distance between the masses you decrease the force by a factor of 1/2.