What must be activated for the landing light to function properly?

For the landing light to function properly, it is essential for the landing light switch to be activated. This switch specifically controls the power supply to the landing light, allowing it to turn on and illuminate the area in front of the aircraft during landing or taxiing phases. Without this activation, the landing light would remain off, regardless of other systems being engaged.

The other options mentioned, while they are important components in the operation of the aircraft, do not directly affect the functionality of the landing light. The fuel switch is related to the engine operation, the landing gear switch is involved in the deployment and retraction of the landing gear, and the external power switch regulates external electrical power to the aircraft systems. However, none of these switches have a direct impact on the operation of the landing light independent of the landing light switch itself.