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.

[EX Q]: Fact: a barometer is used to measure air pressure.
[EX A]: air pressure headache.

[EX Q]: Fact: the Earth being tilted on its rotating axis causes seasons.
[EX A]: Seasons are annual.

[EX Q]: Fact: Ancestors of hagfish are thought to have been the earliest vertebrates.
[EX A]:
Vertebrates.