Final answer:
Dynastic monarchies in the modern era are primarily based on hereditary rule.
Step-by-step explanation:
In the modern era, dynastic monarchies are mainly based on c) Hereditary rule. In a dynastic monarchy, a single person (monarch) rules until they die or abdicate the throne, and they usually claim the title through hereditary succession or divine appointment. While some modern monarchies have limited political power, hereditary rule remains a common characteristic.