Final answer:
The synovial membrane (option C) forms the inner lining of the capsule of a freely movable joint and secretes synovial fluid, which lubricates the joint to allow for smooth movement.
Step-by-step explanation:
The membrane that forms the inner lining of the capsule of a freely movable joint, and secretes synovial fluid, is known as the synovial membrane. This membrane is an example of connective tissue, specifically a connective tissue membrane, which lines the cavities of freely movable joints, also known as synovial joints. The synovial fluid produced by the synovial membrane serves as lubrication, which is critical to reducing friction between the bones within the joint cavity, allowing for smooth movement.
The correct answer to what the synovial membrane secretes is synovial fluid, a thick, lubricating fluid that fills the interior of a synovial joint. Additionally, the synovial membrane provides nourishment to the articular cartilage, which is important because this cartilage lacks blood vessels and relies on the synovial fluid for nutrients.