In a cable belt conveyor, the primary function of the cable is to support the conveyor belt and provide the motion needed to transport materials. The cable runs along the length of the conveyor and is driven by a motor, pulling the belt along with it. This setup ensures efficient movement over long distances, often in mining or industrial applications. Options like increasing lateral stiffness, tensile strength, or minimizing elongation are not the primary roles of the cable, as those are more related to the belt's material properties.
Thus, the correct answer is Support and provide motion to the belt.