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: Invertebrates are animals that lack a vertebral column, or backbone.
Invertebrate.

Fact: gravity pulls objects towards planets.
gravity objects planets.

Fact: a tape measure is used to measure length.

Length.