Definition: In this task, you are given two facts, and a multiple-choice question. Based on the given facts, answer the question with index of the correct option (e.g, "A").
Input: Fact1: fog is formed by water vapor condensing in the air, Fact2: Fog is essentially very low clouds, consisting of water vapor cooling and beginning to condense., Question: What happens when water vapors cool down? (A) colder weather (B) Fog is formed (C) Heat energy (D) evaporation (E) chemical changes (F) Something to move (G) prolactin release (H) Energy.
Output:
B