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 Input:
Fact: when electricity flows to a light bulb , the light bulb will turn on.

Ex Output:
electricity electrons.


Ex Input:
Fact: Cells vary in size as well as shape, but all cells are very small.

Ex Output:
Cells are functional unit.


Ex Input:
Fact: Temperature falls from lower to higher altitudes.

Ex Output:

altitude mountain.