On page 39 it explains that conducting materials. If some part of the external circuit is composed of an insulating material— for example, if there’s an air gap in the circuit—it’s an open circuit. An electric current will flow through a circuit only if the circuit is closed. A common method of controlling the flow of current through a circuit is to include a device called a switch. Current will flow through the circuit when the switch is closed and will stop flowing when the switch is open.
So your answer is A. The switch within the closed circuit is opened
