Question

question 21 (1.3 points) an example of a pivot joint is the articulation of the femur with the acetabulum proximal radius and the ulna ribs with the sternum first metacarpal and carpal bones

Explanation:

A pivot joint allows for rotation around a central axis. The joint between the proximal radius and the ulna (radioulnar joint) is a pivot - type joint which enables the rotation of the forearm for movements like pronation and supination. The other options do not represent pivot joints. The femur with the acetabulum is a ball - and - socket joint, the ribs with the sternum are cartilaginous joints, and the first metacarpal and carpal bones form a saddle joint.

Answer:

The proximal radius and the ulna