Final answer:
When the switch is open, no current flows through the circuit and the bulbs do not light up. Bulbs A, B, and C will all have the same brightness when the switch is open.
Step-by-step explanation:
When the switch is open, no current flows through the circuit and the bulbs do not light up. This is because an open switch breaks the flow of electrons, causing the circuit to be incomplete. Bulbs A, B, and C will all have the same brightness when the switch is open, which is no brightness at all.