What is the only bone in the body that does not articulate with another bone?

Rationale:
A. This is the visible part of the hair above the skin’s surface. It is made of keratinized cells and does not have the ability to contract or move.
B. This is the portion of the hair located below the surface of the skin within the follicle. Like the shaft, it does not control hair movement.
C. The follicle is the structure in the dermis that surrounds and nourishes the hair root, providing the base for hair growth. While important for hair formation, it does not cause the hair to stand erect.
D. The arrector pili are small bands of smooth muscle fibers attached to hair follicles. When these muscles contract (in response to cold, fear, or emotional stimuli), they pull the hair follicle upright, causing the hair to "stand on end" (a phenomenon known as piloerection or "goosebumps").

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.