Gliding joints, such as those found in the wrist,
a. allow the wrist to rotate.
b. are a type of synovial joint.
c. are essentially ligaments.
d. offer the greatest degree of movement

The answer is letter B.  

Gliding joints are a common type of synovial joints that form between bones that meet at flat or nearly flat surfaces. They allow the bones to glide past one another in any direction --- up and down, left and right, and diagonally. Rotations can be performed through these joints but are only in a limited way because of the shape of the bones and the joint capsule’s elasticity that surrounds the joint. The gliding joints in the human body are the elbows, the knees, the hips, and the wrists. 

Is there any choices ?