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: Animals may compete for territory, water, food, or mates.
Example Output: animal competition.

Example Input: Fact: sand dunes are formed by the wind transporting and depositing sand.
Example Output: sand dune formation desert.

Example Input: Fact: nuclear reactions in stars causes stars to produce light.
Example Output:
light contains photons.