The most numerous and versatile of all the body's joints are

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. The adult human skeleton typically consists of 206 bones, including the axial and appendicular skeletons. This total provides structural support, protection for vital organs, and facilitates movement.
B. 110 is too low and does not account for all bones in the adult skeleton.
C. 126 represents approximately the number of bones in the appendicular skeleton alone, not the entire body.
D. 80 corresponds roughly to the number of bones in the axial skeleton only, not the full adult skeleton.