The words "monarch," "arch-enemy," and "architect" have a common meaning in that they all refer to a primary person in a situation. In this context:
- Monarch refers to a primary ruler or leader in a kingdom.
- Arch-enemy indicates someone who is a principal enemy or main adversary.
- Architect denotes the chief designer or planner behind a building or project.
So, the correct answer is: Refer to the primary person in a situation.