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: treating water is used to remove harmful substances before drinking.
boiling water treat.

Fact: Bird eggs have hard, calcium carbonate shells.
Bird eggs have hard, calcium carbonate shells.

Fact: an animal requires air for survival.

air nitrogen oxygen.