Answer:
Grown, free men.
Step-by-step explanation:
Only people who could be citizens of Rome and the empire are the grown, free men who were never enslaved.
Men who were born to parents from Rome who were free at the time of his birth could, at the age of 18, become the citizen. They should have never been enslaved themselves, in order to gain citizenship.
Women, foreigners, and slaves did not have permission to become citizens of Rome. Women and slaves were not considered to be as important and were considered to be lower class. Aliens and foreigners were outsiders who did not deserve the citizenship of Rome.