The correct option is A Fluid filled synovial cavity between two bones - Joint between atlas and axis
The joint between atlas and axis is a pivot joint, a type of synovial joint. synovial joints are characterized by the presence of fluid-filled cavity between the articulating surface of the two bones. Gliding joints are synovial joints and filled with synovial fluid, these joints allow the bones to glide past one another in any direction along the plane of the joint – up and down, left and right, and diagonally and is not limited. Sutures are only found in the skull. A thin layer of dense fibrous connective tissue binds the articulating bones and they are not fluid filled joint.
Although the knee joint is a synovial joint the characteristics describing the knee joint as a fluid cartilage is incorrect.