What situation would cause an aircraft to pitch up?

When analyzing the scenario where an aircraft pitches up, it's essential to understand how the control surfaces, particularly the elevator, work. The elevator is located on the horizontal stabilizer at the tail of the aircraft and is primarily responsible for controlling the pitch attitude.

When the elevator is deflected upwards (known as a "forward movement of the elevator"), it increases the angle of attack of the tail, which in turn causes the nose of the aircraft to rise. This upward movement directly influences the aerodynamic forces acting on the aircraft, leading to a pitching motion where the aircraft's nose moves upward.

This action is fundamental for maneuvering the aircraft, allowing pilots to initiate climbs, increase altitude, or transition to other flight attitudes. Thus, the forward movement of the elevator is the most direct action that results in an aircraft pitching up.

In contrast, increased throttle primarily affects the aircraft's speed and may induce a pitch-up if airflow increases enough to generate lift, but it is not the direct control input that causes a pitch change. Decreased altitude does not inherently cause a pitch change; it's more about the aircraft's interaction with lift. The ascension of the center of gravity is not a manageable control input in flight and does not directly equate to an aircraft's