Which of the following is a type of hydraulic pump?

All of the options listed—screw pump, gear pump, and piston pump—are indeed types of hydraulic pumps.

A screw pump operates by utilizing two or more screws that turn continuously, creating a vacuum that moves fluid through the pump. The design is effective for handling high-viscosity fluids and provides a consistent flow rate.

A gear pump uses meshing gears to pump the fluid. As the gears rotate, they trap fluid between them and the pump casing, moving it from the inlet to the outlet. These pumps are commonly used for their simplicity and reliability, especially in industrial applications.

A piston pump operates using reciprocating pistons to create pressure and move hydraulic fluid. Depending on the design, piston pumps can provide high pressure and are efficient in their operation, making them suitable for applications requiring significant force.

Therefore, since all three options represent legitimate types of hydraulic pumps, the correct choice encompasses all of them.