Which factor can cause a decrease in lift?

A decrease in lift is influenced by various aerodynamic factors, and one significant factor is a reduction in airspeed. Lift is generated primarily by the airflow over the wings, and its magnitude is affected by the speed of that airflow relative to the wings. When airspeed decreases, the amount of air flowing over the wing's surface drops, leading to a reduction in lift. This drop in lift can become critical during slower flight conditions, such as during approach or landing phases, where maintaining sufficient lift is essential to prevent a stall.

In contrast, increasing the angle of attack generally increases lift up to a certain point, as it allows the wing to intercept more airflow, up to the critical angle where stalling occurs. Increasing air density is beneficial for lift generation since denser air provides more molecules for the wings to interact with. Reducing wing area impacts lift negatively, but it is not as directly impactful as the decrease in airspeed, which has an immediate and measurable effect on how much lift the wings can produce. Therefore, the direct relationship between decreased airspeed and reduction in lift explains why this is the correct choice.