Which atmospheric conditions will cause the true landing speed of an aircraft to be the greatest?

The true landing speed of an aircraft is influenced significantly by atmospheric conditions, particularly temperature and humidity, due to their effects on air density. High temperature and high humidity reduce air density. When the air is less dense, the lift generated by the wings decreases, requiring the aircraft to fly at a higher true airspeed to produce enough lift for landing.

In the case of high temperature combined with high humidity, the air density is at its lowest among the choices provided. Consequently, the aircraft needs to maintain a greater true airspeed to achieve the necessary lift during landing as compared to other atmospheric conditions like low temperature or standard humidity levels.

This is why high temperature paired with high humidity results in the greatest true landing speed, as the aircraft's performance is more significantly affected by the lower air density in such conditions.