the knee is what type of joint?\na. hinge\nb. ball-and-socket\nc. pivot\nd. gliding

Brief Explanations:

Hinge joints allow movement along one plane (flexion and extension), which matches the knee's function. Ball-and-socket joints (e.g., hip) allow multi-directional movement, pivot joints (e.g., neck) enable rotation, and gliding joints (e.g., wrist bones) allow sliding between flat surfaces.

Answer:

A. Hinge