The correct option is a. Divergent plate boundaries. Mountain ranges do not form at divergent plate boundaries. Instead, these boundaries are characterized by the creation of new oceanic crust through seafloor spreading, which causes the plates to move away from each other. Mountain ranges are formed at convergent plate boundaries, where two plates collide and the heavier plate subducts beneath the lighter plate, leading to volcanic activity and the formation of mountains. Transform plate boundaries are where two plates slide past each other, and they do not typically result in the formation of mountains. However, they can contribute to the formation and movement of existing mountain ranges by causing horizontal displacement along faults.