The primary muscle of breathing is the:

Rationale:
A. Cartilaginous joints are connected entirely by cartilage (such as the pubic symphysis or intervertebral discs). They allow limited movement but do not make up the majority of joints in the body.
B. Fibrous joints are connected by dense connective tissue and are mostly immovable (such as sutures in the skull). They are important for stability but are relatively few compared to synovial joints.
C. Synovial joints are the most numerous type in the body and allow the greatest range of motion. Examples include the shoulder, hip, knee, and elbow. They are characterized by the presence of a joint cavity filled with synovial fluid, articular cartilage, a synovial membrane, and supporting ligaments. Their structure allows movements such as gliding, rotation, flexion, extension, abduction, and adduction.
D. Synarthroses refers to immovable joints (such as sutures), which are a subset of fibrous joints. They provide stability but are not the majority type of joint in the body.

Rationale:
A. Hinge joints, like the elbow and knee, allow movement in only one plane (flexion and extension) and therefore have a limited range of motion.
B. Condyloid joints, such as the wrist, permit movement in two planes (flexion/extension and abduction/adduction) but do not allow full rotation.
C. Ball-and-socket joints, including the shoulder and hip, consist of a spherical head fitting into a cup-like cavity, allowing movement in multiple planes—flexion, extension, abduction, adduction, rotation, and circumduction—providing the greatest range of motion of all joint types.
D. Saddle joints, like the thumb carpometacarpal joint, allow movement in two planes with some rotation but still offer less overall mobility than ball-and-socket joints.