Final answer:
The squat is classified as a (B) compound movement because it involves multiple joints and a significant amount of musculature across those joints, particularly flexion and extension of the hip and knee joints.
Step-by-step explanation:
The squat is a compound movement due to the several joints involved (ankles, knees, and hips) and the large amount of musculature used. When performing a squat, multiple joints and muscles work in synergy to execute the movement. Synovial joints like the hip and knee joints allow for various types of movements, and muscles around these joints act as agonists, antagonists, or synergists depending on the movement.
For example, during a squat, the hip and knee joints go through flexion when lowering the body and extension when raising it back up. These movements at the hip and knee joints are crucial for the squat, illustrating why it's classified as a compound movement rather than an isolation, unilateral, or concentric exercise.