The first strings of holiday lights were manufactured as series circuits. which explains why this method is no longer used? a. in order for a series circuit to remain closed, enabling electrons to flow, all lights must work. b. in a series circuit, if all lights work the circuit remains open, but if one burns, it closes the circuit. c. lightbulb manufacturers stopped making lightbulbs that could be wired in series. d. series circuits require more wire to keep electrons flowing between lightbulbs.