Final answer:
Increasing height is the option that would increase an object's potential energy, as it increases the potential for the object to do work due to gravity when higher up.
Step-by-step explanation:
The option that would increase potential energy is d) Increasing height. Potential energy is energy that is stored in an object due to its position, condition, or composition. Raising an object to a greater height increases its gravitational potential energy because it has the potential to do more work due to gravity when it is higher up. Activities such as speeding up increase kinetic energy, while slowing down does work as it converts kinetic energy to other forms, but it doesn't increase potential energy.
The other concepts mentioned, such as increasing temperature or compressing an object, relate to the internal energy of the system but not directly to its gravitational potential energy.