Question

when one light in a string of holiday lights goes out and the rest of the string also goes out, what type of current is used? A)Open Circuit B)Series circuit C)Combination circuit D)Parallel circuit

Answer 1

That's a SERIES circuit.  The lights are wired in such a way that
there is only one path for the current to take, and the current for
any bulb must flow through all of them.  So if any bulb burns out
and current can't pass through it, then current can't flow through
ANY bulb, and they all go out. 

Answer 2

I think it is open circuit