What is the smallest component of the empennage that controls the nose's upward and downward movement?

The correct choice is the elevator, which is the smallest component of the empennage responsible for controlling the aircraft's nose's upward and downward movement. The elevator is typically located at the trailing edge of the horizontal stabilizer and functions by changing the angle of attack of the stabilizer. When the pilot moves the control yoke or stick forward or backward, the elevator deflects up or down, respectively, causing the tail of the aircraft to move in the opposite direction. This movement alters the airflow over the horizontal stabilizer, resulting in pitch changes: deflecting the elevator up causes the nose to rise, while deflecting it down leads to a descent.

In contrast, the horizontal stabilizer serves as a fixed surface that provides stability but does not actively control movement. The rudder, found on the vertical stabilizer, primarily manages yaw, or side-to-side movement, and does not influence pitch. The vertical stabilizer provides directional stability but does not affect the nose's elevation directly. Understanding the role of each component within the empennage helps clarify why the elevator specifically is responsible for pitch control.