________ is the ability to do work.

In mechanics, energy is defined as a system's capacity to perform work, while force is the push or pull exerted on an object that can change its state of motion. Work is done when a force acts through a displacement, so force and energy are related but are not the same physical quantity -- one is an interaction, the other a capacity.

The blank asks for the single term whose standard definition matches 'the ability to do work.' Among the four options, exactly one physical quantity carries that definition in standard mechanics; the others describe a different quantity, a mixture of quantities, or reject all the candidates.

• Force is the interaction responsible for producing work when it acts through a displacement, but a force with no resulting displacement (for example, pushing against an immovable wall) does zero work -- so force by itself is not a measure of the capacity to do work.

• 'Energy and force both' merges two quantities with different SI units (joules for one, newtons for the other) and different physical roles into a single answer, even though the blank calls for one specific term.

• 'None of these' would be correct only if none of the other three options matched the definition being tested, which is not the case here since one of them corresponds to it exactly.

Therefore, the term defined as the ability to do work is Energy.