In which situation may the surface remain dry instead of forming dew?

Correct answer: Surface temperature remains well above the dew point

Correct answer: A. Dew requires the surface or the air immediately touching it to cool to the dew point. At or below that threshold, the air becomes saturated and excess water vapour can condense on the surface. If the surface temperature remains well above the dew point, the nearby air is not cooled enough to reach saturation, so liquid droplets do not form and the surface may remain dry. A is therefore correct. B is not the best answer because air very close to saturation makes dew more likely, especially if only slight additional cooling occurs. C is wrong because a calm, clear night usually favours radiational cooling and therefore increases the chance of dew. D is wrong because rapid cooling of grass can bring it to the dew point and promote condensation. Memory cue: no dew without reaching the dew-point threshold. “Cool surface plus moist air” favours dew; a warm surface above the threshold prevents it.