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: Secondary meristem is located within and around the vascular tissues.
Example Output: Secondary meristem.

Example Input: Fact: when a cooler object touches a warmer object , thermal conduction occurs.
Example Output: conduction heat.

Example Input: Fact: Echinoderms have a unique water vascular system with tube feet.
Example Output:
echinoderm vascular.