Which answer choice best describes the difference between folded mountains and fault-block mountains? a. folded mountains form only at divergent plate boundaries, whereas fault-block mountains form only at convergent plate boundaries. b. folded mountains form only at convergent plate boundaries, whereas fault-block mountains form only at divergent plate boundaries. c. folded mountains form when segments of earth's crust are bent and doubled over, whereas fault-block mountains form when stress causes pieces of earth's crust to be thrust upward to higher elevations. d. folded mountains form when stress causes pieces of earth's crust to be thrust upward to higher elevations, whereas fault-block mountains form when segments of earth's crust are bent and doubled over.