Answer:
C) Unscrew one light. If the other lights turn off, it's a series circuit.
Explanation:
THIS IS THE COMPLETE QUESTION BELOW;
A strand of 10 lights is plugged into an outlet. How can you determine if the lights are connected in series or parallel? A) Unscrew one light. If the other lights stay on, it's a series circuit. B) Unplug the strand. If the first light stays on, it's a series circuit. C) Unscrew one light. If the other lights turn off, it's a series circuit. D) Cut the strand in half. If the plugged in half stays on, it's a series circuit.
SERIES CIRCUIT
In this circuit, the components there are in the same path, the entire circuit has the same current, each of the components posses different voltage drop. Hence, failure of one components to work, there will be break in entire circuit then other components cease to work.
PARALLEL CIRCUIT
This circuit has equal voltage drop across all the components, any problem in a component will not has effect on other components.
Therefore, if one want to determine if a light connection is in series or in parallel, one of the light can be unplugged if others stop working it means it's series, if other works it's parallel.