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: condensation is when change from a gas into a liquid by reducing heat energy.
Example Output: condensation gas liquid.

Example Input: Fact: Most ecosystems get energy from sunlight.
Example Output: ecosystem habitat.

Example Input: Fact: Most arthropods are insects.
Example Output:
arthropod.