Final answer:
If an aircraft's center of gravity is too far aft, it can result in decreased stability and possibly a flat spin, making it challenging to control the aircraft.
Step-by-step explanation:
When the center of gravity (CG) of an aircraft is too far aft or rearward, it can lead to decreased stability and control of the aircraft. The correct answer to the question of what happens if the CG is too far aft is Option A: A flat spin can occur. This situation can be very dangerous as it makes the aircraft very sensitive to control inputs and may result in an aircraft entering into a flat spin, which is a type of stall/spin that is difficult to recover from. In this condition, the aircraft rotates around its center of gravity with a high angle of attack and low airspeed, making it less responsive to control inputs. Having the CG too far aft does not make the aircraft more stable (Option B) or cause it to climb at a steeper angle (Option C); nor does it necessarily lead to reduced lift (Option D).