What factors primarily affect the stall speed of an airplane?

The stall speed of an airplane is primarily affected by weight and bank angle, which makes this answer the most accurate among the choices provided.

As an aircraft's weight increases, whether due to additional passengers, cargo, or fuel, the stall speed also increases. This is because a heavier airplane requires more lift to maintain level flight. Since lift is directly related to the speed of the aircraft, a higher weight necessitates a higher stall speed to avoid a stall condition.

Additionally, bank angle plays a significant role in stall speed. When an airplane banks, the load factor increases due to the effect of gravitational and centrifugal forces. A higher load factor requires a greater amount of lift to keep the airplane in a coordinated turn. Hence, as the bank angle increases, the stall speed also increases proportionally.

Understanding these factors is crucial for pilots to ensure safety and control during flight, particularly in maneuvers involving turns or heavy loads, where stall speed considerations become increasingly critical.