What is the primary function of the pelvis in the human skeleton?

The primary function of the pelvis in the human skeleton is to form a basin-shaped structure that supports various organs, particularly those in the lower abdomen, such as the bladder, reproductive organs, and parts of the digestive system. This basin shape is crucial for maintaining the structural integrity of the body while allowing for flexibility and mobility, especially in activities like walking, running, and even childbirth.

The pelvis serves as an attachment point for the spine and the lower limbs, playing a significant role in weight-bearing and balance. Its design not only contributes to its supportive functions but also plays an essential role in protecting the organs housed within it from injury. In addition, the pelvic structure aids in facilitating a stable base for movement of the legs.

In contrast, the other options do not accurately reflect the pelvis's role: the pelvis does not support the upper limbs, protect the brain (which is the role of the skull), or directly facilitate knee movement (which is primarily the function of the femur, tibia, and associated ligaments). Thus, the correct answer highlights the pivotal supportive role the pelvis plays in the human skeletal system.