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: Cells vary in size as well as shape, but all cells are very small.
Example Output: Cells are functional unit.

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

Example Input: Fact: Playing is just one of many ways that mammals and other animals learn how to behave.
Example Output:
animal kitten.