Write the next sentence in the following story.

How to charge a power bank
Check the led lights to see when your power bank needs charging.
While a power bank can be charged at any time, unnecessary charging may decrease its lifespan. Most power banks have 4 led lights on the side.

Pick your answer from: a). If a turn turns out to be green, the power bank might have disabled the battery. Determine what kind of lights to charge.; b). When your power is charging, after you turn on the lights, the led lights appear once or twice. If your power bank has only 4 led lights, you can try charging batteries with matching led bulbs.; c). The lights are needed to charge your power system regularly. Apply the led light when it turns off and you can charge it more readily.; d). The lights will shut off as the battery diminishes. Wait to charge your power bank until only 1 or 2 lights are on.;. The answer should be
d).