Explanation: In the field of aerospace engineering, the materials used in the construction of airplane body parts are crucial for ensuring the aircraft's performance, safety, and longevity. Two of the most commonly used materials in this context are aluminum and titanium.
**Aluminum:**
Aluminum is widely used in the aerospace industry due to its excellent properties. It is lightweight, which is critical for reducing the overall weight of the aircraft and improving fuel efficiency. Additionally, aluminum has a high strength-to-weight ratio, meaning it can provide the necessary structural integrity without adding excessive weight. It is also highly resistant to corrosion, which is essential for the longevity of the aircraft, especially when exposed to the harsh conditions of high altitudes and varying climates. Aluminum alloys, such as 2024 and 7075, are specifically designed for aerospace applications and are used in various parts of the aircraft, including the fuselage, wings, and landing gear.
**Titanium:**
Titanium is another important material used in aircraft construction. It is known for its exceptional strength-to-weight ratio, which is even higher than that of aluminum. Titanium is also highly resistant to corrosion and can withstand high temperatures, making it suitable for parts that are exposed to extreme conditions, such as engine components and landing gear. The use of titanium in aircraft construction helps to reduce weight and improve performance while maintaining the necessary structural integrity. Common titanium alloys used in aerospace include Ti-6Al-4V, which is widely used for its excellent mechanical properties and corrosion resistance.
**Coal:**
Coal, on the other hand, is not used in the construction of airplane body parts. Coal is primarily used as a fuel source for power generation and is not suitable for aircraft construction due to its heavy weight and lack of structural integrity. The use of coal in aircraft would significantly increase the weight of the aircraft, reducing its efficiency and performance.
In summary, aluminum and titanium are the primary materials used in the construction of airplane body parts due to their lightweight, high strength, and corrosion resistance. These properties make them ideal for aerospace applications, ensuring the aircraft's performance, safety, and longevity. Coal, being a heavy and structurally unsuitable material, is not used in aircraft construction. Therefore, the correct answer is (D) Only (A) & (B).