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: a nest is used for protecting young by birds.
bird nest.

Fact: Air pollution harms the respiratory and circulatory systems.
Air pollution caused by.

Fact: Communities consist of populations of different species.

communities work together.