Question 18
Switch A turns lights 1 and 2 on-off or off-on. Switch B turns lights 2 and 4 on-off or off-on. Switch C turns lights 1 and 3 on-off or off-on. White = ON, black = OFF. Switches A, C and B are thrown in turn, with the result that Figure 1 turns into Figure 2. Which of the switches A, B or C must be faulty?
