The contacts of a(n) __________ switch are open until acted on by the operator.

A normally open switch is designed such that its contacts remain open when in their default state, allowing no electrical current to flow through. It requires manual operation by the user to close the contacts, thereby enabling the circuit and allowing current to flow. This is a common design in various applications, such as light switches and many control systems, where the action of pressing or toggling the switch is needed to control the operation of a device.

In contrast, the other types of switches mentioned do not match this definition. A normally closed switch, for instance, has contacts that are closed by default and allows current to flow until the operator opens the switch. This means it functions oppositely to a normally open switch. The terms "normally simulated" and "adjacent" do not pertain to standard switch terminology, further supporting that normally open is indeed the correct description for the switch in question.