What is the limitation regarding operation of the wing anti-ice system?

The correct answer highlights the precise operational limits for the wing anti-ice system, which is critical for maintaining aircraft safety in icy conditions. Specifically, the system should be activated during takeoff when temperatures are below 5 degrees Celsius and there is visible moisture present. This is essential because such conditions can lead to ice accumulation on the wings, which adversely affects the aircraft's aerodynamics and performance.

The limitation reflects a specific threshold to prevent ice buildup that could compromise lift and stall characteristics. Activating the wing anti-ice system under these conditions helps to ensure that the wings remain clear of ice, thus enhancing safety during critical flight phases like takeoff.

In contrast, other options either suggest different temperature thresholds or operational procedures that do not accurately reflect the established guideline for safe operation of the wing anti-ice system during takeoff. Understanding these limitations is crucial for pilots and flight crews to ensure safe winter operations.