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.

Example Input: Fact: an automobile engine transforms chemical energy into mechanical energy.
Example Output: automobile engine.

Example Input: Fact: skin is used for breathing air by frogs.
Example Output: air oxygen.

Example Input: Fact: a thermal insulator slows the transfer of heat.
Example Output:
heat transfer causes.