The distance was increasing and the rotational force was decreasing. Why is that?
Use T = rF to explain.

for box A :

gravitational pull is given as

F = G (10) (10) /r²

F = 100 G/r²                                                       eq-1

for Box B :

gravitational pull is given as

F' = G (10) (5) /r'²

F' = 50 G/r'²                                                       eq-2

for Box C :

gravitational pull is given as

F'' = G (10) (15) /r''²

F'' = 150 G/r''²                                                       eq-3

from the diagram , we see that

r = r'

hence F > F'

gravitational pull of box B is greater than gravitational pull of box A.

r'' > r = r'

such that r'' is almost 2 times of r and r'

so F'' = 150 G/(2r'²)

F'' = 37.5 G/r'² = 37.5 G/r²

hence box A has greatest gravitational pull between the objects.

A) the object inbox A would have the strongest gravitational pull because they are close to each other and have more mass.