Answer the following question given this paragraph: 

Hydraulic car lifts also use fluid to transmit pressure and increase force. The lifts are used to raise cars, which are very heavy, so mechanics can work on them from underneath. Controls in airplanes use fluids to transmit pressure and increase force so a flick of a switch can raise or lower heavy landing gear. To see animations of hydraulic systems such as these, go to URLs:.


Q: What kind of systems use fluid to transmit pressure and increase force?

 Choices:

- plumbing systems

- thermal systems

- electromagnetic systems

- hydraulic systems

A:
hydraulic systems
