D. It allows the flow of an electric current in the circuit.
<h3>Why is it important to have a closed circuit?</h3>
Closed circuit allows the flow of current in the circuit from the battery to the bulb. If the circuit is open then the current will not reach to the bulb or other appliances.
So we can conclude that It is important to have a closed circuit because it allows the flow of an electric current in the circuit.
