Which of the following is an example of mechanical control?

Mechanical control refers to methods that physically alter the environment or directly manage pest populations without the use of chemicals. Fences serve as a physical barrier to prevent pests, such as animals, from accessing specific areas, thereby protecting crops or gardens. This action effectively reduces or eliminates pest pressure in a way that is straightforward and tangible, embodying the principles of mechanical control.

Other options address different methods of pest management. Aeration is more about improving soil health and does not directly eliminate pests. Crop selection involves choosing specific species or varieties of plants to minimize pest incidence but does not involve a physical mechanism to control pests. Irrigation is important for plant health but does not specifically relate to controlling pests mechanically.