Final answer:
A monarchy is a form of government where one person, often referred to as a monarch, holds the supreme power. The correct answer to the question is 'c) One person.'
Step-by-step explanation:
To answer the question, 'Monarchy is ruled by ____________.', we must understand what a monarchy is. A monarchy is a form of government where one person, called a monarch, holds supreme power usually for life or until abdication. This ruler can be a king, queen, prince, or princess, and typically claims the right to the throne by way of hereditary succession or, sometimes, through divine appointment.
In some countries, monarchs have ceremonial roles with no real political power, while in others, like absolute monarchies, they hold significant authority.
In the context of the given options for the question, the correct completion of the sentence would be 'c) One person.' Therefore, monarchy is ruled by one person.