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

Example Input: Fact: when water freezes , that water expands.
Example Output: freeze.

Example Input: Fact: radioactive dating is used to determine the age of fossils.
Example Output:
age of fossils geologists.

