An aircraft airfoil is designed to produce lift resulting from a difference in what?

The correct answer focuses on the fundamental principle of aerodynamics that allows an airfoil to generate lift. Lift is predominantly created by the shape and angle of attack of the airfoil, which causes air to move faster over the top surface than the bottom surface. This creates a difference in air pressure due to Bernoulli’s principle, where faster-moving air results in lower pressure.

Thus, having higher air pressure below the airfoil's surface and lower air pressure above is essential for lift generation. The increased pressure below pushes the airfoil upward into the lower pressure area above, resulting in lift.

The other options do not accurately represent this principle. Equal air pressure on both surfaces would not create the necessary pressure differential for lift, and the temperature differences mentioned in the last option are not directly related to how airfoil lift is generated. Therefore, the selected answer correctly aligns with the aerodynamic theory of lift generation.