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.

Fact: Behaviors can be learned through play.
Behaviors.

Fact: a flashlight converts chemical energy into light energy.
battery chemical energy.

Fact: Antigens are molecules that the immune system recognizes as foreign to the body.

Antigens are.