The variables that affect the gravitational force between two objects are:
- mass: The gravitational force increases with the mass of the objects.
- distance between them: The gravitational force decreases as the distance between the two objects increases.
The other options do not affect the gravitational force:
- volume: Volume does not directly affect gravitational force; only mass does.
- air pressure: Air pressure does not have a direct effect on gravitational force.
- speed: The speed of the objects does not affect the gravitational force between them.
So, the correct selections are mass and distance between them.
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