instruction:
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.
question:
Fact: Prokaryotes are single-celled organisms that lack a nucleus.
answer:
Prokaryotes.


question:
Fact: Some pelycosaurs gave rise to a group of animals called therapsids.
answer:
pelycosaurs.


question:
Fact: Population density is the average number of individuals per unit of area or volume.
answer:

population density high.