What must be done to frost on the wing of an airplane before takeoff?

Frost on the wings of an airplane can significantly impair its aerodynamic performance by disrupting airflow over the wing surfaces. This disruption can lead to a reduction in lift and an increase in drag, which can result in poor handling characteristics and a potentially unsafe takeoff.

To ensure safety and proper flight performance, it is essential to remove any frost before takeoff. This is typically accomplished through procedures such as de-icing or using heated surfaces, which will restore the wing's smooth contour and allow for optimal airflow during flight. By eliminating frost buildup, pilots can help ensure that the aircraft will behave predictably and safely during the critical phases of takeoff and climb-out.

The other options do not address the critical problems associated with frost on the wings. Frost should never be left intact, as it would compromise the aircraft's stability and handling. Sanding it off, while it might appear to remove the frost, is not a standard or effective method for preparing the aircraft for flight. Allowing frost to remain is unacceptable, as it poses a real danger to flight safety. Therefore, removing the frost is the only appropriate action to take prior to takeoff.