The correct answer is: A. A month.
The Joint Sighting Committee (JSC) is a committee that is responsible for inspecting the visibility of signals at airports. The JSC is made up of representatives from the airport, the air traffic control authority, and the airline. The JSC is required to inspect the visibility of signals at least once a month.
The purpose of the JSC’s inspections is to ensure that the signals are visible and that they are in good working order. The JSC’s inspections also help to identify any potential problems with the signals so that they can be fixed before they cause an accident.
The JSC’s inspections are an important part of the safety of air travel. By inspecting the visibility of signals on a regular basis, the JSC helps to ensure that pilots can see the signals and that they are in good working order. This helps to prevent accidents and to keep air travel safe.
The other options are incorrect because they are not the frequency at which the JSC is required to inspect the visibility of signals.