The correct answer is: Energy.
Energy is the capacity to do work. It is a fundamental property of matter and energy is always conserved. Energy can be converted from one form to another, but it cannot be created or destroyed.
Power is the rate at which energy is used or converted. It is measured in watts, which are joules per second.
Force is a push or pull that acts on an object. It is measured in newtons, which are kilograms times meters per second squared.
Strength is the ability to exert force. It is measured in pounds-force or newtons.
In conclusion, the capacity to do work is termed as energy.