Final answer:
An airplane designed to fly at high altitudes may include an added tank of oxygen to mix with the fuel for combustion due to thinner air at high elevations. This modification ensures the internal combustion engines function efficiently despite the lower oxygen density. So the correct option is C.
Step-by-step explanation:
An airplane designed to fly at high altitudes may have certain adaptations to ensure performance and safety at those elevations. Considering the physics and engineering involved in aircraft design, the correct answer to the question concerning high-altitude airplane design is:
Option C: an added tank of oxygen to mix with the fuel for the combustion reactions.
Aircraft operating at high altitudes could require additional oxygen due to thin air, as internal combustion engines need oxygen for fuel combustion. Oxygen at these heights is less densely packed, thus necessitating an added tank of oxygen onboard to maintain efficient engine operation. Moreover, the development process of aircraft usually involves a significant amount of research and development (R&D) to optimize various aspects of the airplane, such as engine placement and aerodynamics, as well as to ensure that safety measures like adequate oxygen supply for combustion and pressurization are in place. HighFlyer Airlines, for example, would investigate various methods through R&D to increase cabin space without compromising the operating costs and safety of the aircraft.