What must be done when type II, III, or IV anti-icing fluids have been applied?

When type II, III, or IV anti-icing fluids have been applied, it is essential to select wing anti-ice ON prior to thrust increase for takeoff. This action is crucial because these fluid types are designed to provide protection against the formation of ice on the wings and other critical surfaces, but they are not effective at retaining this protection once the aircraft is in motion and especially as it prepares for takeoff.

Activating wing anti-ice ensures that the wings continue to remain free of ice during the most critical phase of flight. Ice accumulation can adversely affect an aircraft's aerodynamic performance, impair lift, and increase drag, which could potentially lead to hazardous situations during takeoff. Ensuring that the wings are heated prevents any latent ice from forming on the wings after the anti-icing fluids have been applied.

The other options do not adequately address the critical requirements following the application of these anti-icing fluids, particularly in preparing the aircraft for a safe takeoff in icy conditions. Turning off all anti-ice systems or doing nothing would leave the wings vulnerable to ice formation, and only checking the weather report does not actively mitigate the risks associated with existing ice, thus highlighting the importance of selecting wing anti-ice ON before takeoff thrust.