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: if an object is made of a material then that object has the properties of that material.
Material is a substance.

Fact: Many corals secrete an exoskeleton that builds up to become a coral reef.
coral exoskeleton is made of carbonate.

Fact: changes in the pH of soil can cause plants to die.

change ph soil.