When must flight attendants be seated with their seat belts fastened?

Flight attendants must be seated with their seat belts fastened during taxi, take-off, and landing due to safety regulations that are designed to protect them in times of unexpected turbulence or other scenarios requiring sudden maneuvers.

During taxi, the aircraft is still in motion, and potential hazards can arise from other ground traffic or sudden changes in direction. Fastening seat belts helps ensure that flight attendants remain securely in their seats to manage any unforeseen circumstances.

During take-off and landing, the aircraft experiences heightened risk due to changes in altitude and speed, potentially increasing the likelihood of turbulence. Keeping seat belts fastened in these phases is a critical safety precaution that mirrors the same requirement for passengers.

Thus, the correct answer reflects the essential safety procedures outlined by aviation regulations, which mandate that flight attendants remain secured in their seats during these critical operational phases of flight to ensure their safety and the overall safety of the passengers.