If grass surface becomes colder than the air, why can dew form?

Correct answer: Because air near the surface can cool to dew point

Answer: A. Dew forms when water vapour changes into liquid droplets on a cool surface. At night, grass may lose heat and become colder than the air above it. The thin layer of air touching the grass is then cooled. If this air reaches its dew point, it cannot hold all its water vapour, so some vapour condenses on the grass as dew. A is correct because it describes both the cooling and the dew-point condition. B is wrong: grass does not destroy water vapour; it provides a cold surface for condensation. C is wrong because grass does not always freeze, and ice forms only when temperatures are at or below freezing. D is wrong because warm air can hold more vapour and does not explain the cooling needed here. Memory cue: cool surface plus dew point produces dew.