By Newton's Law of Universal Gravitation.
F = GMm/r²
Where F is Force of Gravitation, M = Mass of first object, m = mass of second object, r = distance of separation
From the formula, you can see that if the masses, M and m, increased, the value of F would definitely increase as well.
And if r increased the value of F would be reduced because you would be dividing by a bigger number, but when the value of r is decreased the value of F would be increased, because you would then be dividing by something smaller. Note the r is at the denominator of the formula.
So F would increase if there was increase in Masses and decrease in distance.
So the answer is C. a and b.