In this task, you need to write a topic word from the given fact. The topic word must have at least one word overlap with the given fact. The topic word often involves adding a new word from a related concept. In your topic word, use at least one word from the given fact. Topic words with two or more words work best.

Example Input: Fact: if gas is heated then that gas will expand.
Example Output: expand heat density gas.

Example Input: Fact: Mating is generally preceded by courtship.
Example Output: animal courtship.

Example Input: Fact: transpiration is when water vapor moves from plants into the atmosphere.
Example Output:
atmosphere air.