It means three light are connected in a series. Then if I unscrew one battery from the circuit, the left lightbulbs are going to be off, because three bulbs and the batteries were connected in a series. Also, if I connect the ammeters in the space that the lightbulb was located, the amphere s measured. It means that the electricity they are connected in a series, because electricity doesn’t flow when some part is ruined are broken.
Even though, we unsrew the light bulb that was parallel with other light bulbs, the other left light bulbs are not going to be turned off.
The light bulbs that are in parallel get weaker current than the series one, so series one is going to be more powerful than the paralle one.