Which two characteristics increase the strength of the gravitational force between two objects?
A. Having centers that are closer together
B. Having hollow centers
C. Having greater masses
D. Having greater charges

The answer is A and C.

Explanation:

Only two factors are relevant when dealing with the gravitational force between two objects - their mass and their distance apart from one another. Gravity's force is proportional to the product of the masses of the two objects and is inversely proportional to the square of the distance between them.

measuring things 1 litre of water