Why may more dew appear on an exposed car roof at night than under a tree?

Correct answer: The exposed surface cools more by radiation

Answer: B, because the exposed roof can lose more heat by radiation to the clear night sky. During a clear night, an object with an unobstructed view of the sky emits thermal radiation and cools. If its surface temperature falls to the dew point, water vapour from the nearby air condenses on it as dew. A tree canopy can partly obstruct the sky and reduce this radiative cooling beneath it; the ground and air under the tree may therefore remain relatively warmer, so less dew may form there. Option A is wrong because the tree does not simply create vapour and stop dew; its shade and canopy mainly alter cooling and local conditions. Option C is wrong because a car roof does not create clouds. Option D is wrong because trees do not remove gravity. The key is exposure to the open sky, not the material alone. Memory cue: clear sky plus exposed surface favours stronger night cooling and more dew.