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: Infancy is the period of most rapid growth after birth.
Example Output: Infancy.

Example Input: Fact: treating water is used to remove harmful substances before drinking.
Example Output: boiling water treat.

Example Input: Fact: Cells are the microscopic building blocks of organisms.
Example Output:
building blocks bricks.