Biplanes are aircraft characterized by what feature?

• A. Airplanes with two engines.
• B. Airplanes with two sets of wings.
• C. Airplanes with variable wings.
• D. Single-wing aircraft.

Answer: (B)

Biplanes have two wings, arranged one above the other. This two-wing setup increases the total wing area and lift without needing an extremely long single wing, which was especially helpful with early materials and construction. The upper and lower wings are connected by struts and bracing wires, giving good lift at lower speeds and making the aircraft easier to build in the early days of flight. The trade-off is more drag and structural complexity, which is why later designs often switched to a single-wing layout as engines and materials improved. The other descriptions don’t fit: two engines would be a multiengine aircraft, variable wings refer to wings that extend or retract in span, and a single-wing aircraft is a monoplane.