instruction:
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.
question:
Fact: a ruler is used for measuring the length of an object.
answer:
Length of object.


question:
Fact: Fish have a centralized nervous system with a brain.
answer:
brain allows thinking.


question:
Fact: sand dunes are formed by the wind transporting and depositing sand.
answer:

sand dune formation desert.