Which two systems are commonly used for extending the aerial device?

The correct answer identifies cable and hydraulic systems as commonly used for extending aerial devices. In the context of aerial devices such as fire trucks or cranes, hydraulic systems are widely employed due to their ability to generate significant force and facilitate smooth, controlled movements. They utilize pressurized fluid to extend and retract the aerial device, making them highly effective for heavy lifting and precise positioning.

Cable systems also play a crucial role, particularly in applications that require tensile strength and stability. Cables can be used in conjunction with hydraulic mechanisms to support and guide the movement of the aerial device, ensuring it remains secure during operation.

Other systems like mechanical and electrical, while used in various contexts, do not specifically pertain to the commonality of aerial device extension. Mechanical systems might involve gears and levers, and electrical components typically serve to control operations rather than directly extend the devices. Similarly, options such as wire and elastic are not standard for this purpose, as they do not provide the necessary robustness or safety required in aerial operations.