Question: Which of the following best explains why the pressure inside a high-flying airplane must be controlled?

  Options: 
 A. At high altitudes there is greater atmospheric pressure than on the surface of the Earth.
 B. At high altitudes there is lower atmospheric pressure than on the surface of the Earth.
 C. If the cabin is not pressurized, ozone and other upper atmospheric gases will enter the airplane.
 D. If the cabin is not pressurized, carbon dioxide will escape from the airplane.
Answer: B