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: Energy is passed up a food chain or web from lower to higher trophic levels.
energy calories.

Fact: when a gas in an open container evaporates , that gas spreads out into the air.
air contamination.

Fact: the movement of an air mass over Earth 's surface causes local weather changes.

air mass front.