What can be used to raise and lower the blade of a road grader?

Hydraulic arms are the primary mechanism for raising and lowering the blade of a road grader, making this the correct answer. Hydraulic systems use fluid mechanics to transfer force and create motion, allowing operators to adjust the blade's height with precise control. This capability is essential for grading surfaces accurately, as it allows for adjustments to be made quickly and efficiently while maintaining stability and strength.

In contrast, while gears, levers, and cables may be part of other machinery or tools, they do not provide the same level of effectiveness or precision in this specific application. Gears can facilitate motion but are less effective for fine adjustments needed on a grader's blade. Levers can provide mechanical advantage but would require a more complex system to manage the blade's movement effectively. Cables might be used in some systems but are generally not the preferred method for controlling heavy grader blades due to potential limitations in strength and precision compared to hydraulic systems.