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: Plasma cells are activated B cells that secrete antibodies.
Example Output: antibodies fight infection.

Example Input: Fact: if an animal sweats then that animal 's bodily water decreases.
Example Output: animal human.

Example Input: Fact: rocks interacting with wind over long periods of time causes weathering.
Example Output:
rock limestone.