Which of the following applies to both hydraulic and pneumatic systems?

The correct answer highlights that both hydraulic and pneumatic systems rely on the movement of a fluid, which is essential to their operation. In hydraulic systems, this fluid is typically a liquid, such as oil, which is used to transmit force and energy through the system. In pneumatic systems, the fluid is a gas, most commonly air, which is compressed and used to perform work.

Both systems function on similar principles of energy transfer through fluid movement, allowing them to create mechanical force and perform tasks such as lifting, moving, or operating machinery. Despite the different states of matter involved (liquid for hydraulics and gas for pneumatics), the fundamental concept of fluid movement driving system efficiency remains the same.

The other choices do not accurately capture the essential characteristics that hydraulic and pneumatic systems share. For example, they do not operate using electrical currents, as their primary function is based on fluid dynamics rather than electrical energy. While both systems can generate heat as a byproduct, it is not a defining characteristic relevant to their primary operation. Lastly, the requirement of high-pressure gas applies only to pneumatic systems, not hydraulic ones where high-pressure liquids are used instead.