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: Nephrons are the structural and functional units of the kidneys.
Nephrons cause.

Fact: breaking apart rocks can cause debris.
a hammer can break rock.

Fact: biofuel is used to produce electricity by burning.

biofuel electricity.