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.

Input: Consider Input: Fact: Hydrogen bonds cause water to expand when it freezes.

Output: freezes.


Input: Consider Input: Fact: a vehicle is used for travel.

Output: travel navigation.


Input: Consider Input: Fact: a prism is used for refracting light.


Output: a prism is used for refracting light.