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: when a metal rusts , that metal becomes orange on the surface.

Output: metal iron.


Input: Consider Input: Fact: Passive immunity lasts only as long as the antibodies survive in body fluids.

Output: antibodies protein.


Input: Consider Input: Fact: Ethologists usually study how animals behave in their natural environment.


Output: Ethologists.