Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: A: When air temperature reaches the dew point, water vapor starts condensing. It may form dew (as on the spider web in the opening image), clouds, or fog. Dew forms on solid objects on the ground. Clouds form on tiny particles in the air high above the ground. Fog is a cloud that forms on tiny particles in the air close to the ground. Answer: condense
Output:
When the air temperature reaches the dew point, water vapor starts to do what?