Which two flight controls are primarily used to control the rate of a turn?

The rate of a turn during flight is primarily controlled by the ailerons and the rudder. Ailerons are responsible for controlling the roll of the aircraft, allowing it to bank in the direction of the turn. When the aircraft banks, it creates a vertical lift component that enables the plane to change direction.

While the elevator affects pitch control, it does not play a significant role in the rate of a turn itself. Instead, it is primarily concerned with climbing or descending. The elevator's main function is to control the angle of attack and, consequently, the altitude of the aircraft.

Flaps increase lift but are primarily used for takeoff and landing phases of flight and do not directly impact the rate of turn under normal conditions. The thrust, provided by the engines, can support a turn by maintaining speed but again does not directly control the rate of turn like the ailerons and rudder do.

In essence, the combination of ailerons for banking and rudder for coordination ensures a controlled and effective turn, making this option the correct choice for understanding how to control the rate of a turn in flight.