Which type of materials are commonly used in aircraft structural maintenance?

In aircraft structural maintenance, aluminum, titanium, and composite materials are commonly used due to their desirable properties that align with the demands of aircraft performance and safety. Aluminum is favored for its strength-to-weight ratio, making it ideal for various structural components while keeping the aircraft lightweight. Titanium is known for its exceptional strength and corrosion resistance, which is crucial for components subjected to high stress and harsh environments, such as engine parts and high-performance airframes. Composite materials offer the benefits of high strength, reduced weight, and design flexibility, allowing for the construction of complex shapes and structures that improve aerodynamic efficiency while minimizing the overall structural mass of the aircraft.

The other options, while containing materials that might have specific uses in aviation or other industries, do not accurately represent the primary materials utilized in aircraft structure. For example, wood and plastic are more commonly associated with older aircraft or specific non-structural applications, and concrete, iron, and rubber are not primarily used in aircraft structural components. Therefore, the combination of aluminum, titanium, and composite materials makes option C the most relevant and appropriate choice for aircraft structural maintenance.