<em>Circuit-A</em> <em>is a series circuit</em>. There's only one road that electrons can take to get from one battery terminal to the other one. There's no point in the circuit where an electron has to decide which path to take.
Circuit-B is a parallel circuit. At each of the two 'dimples' across the top, an electron has a choice: It can turn right and go through a bulb, OR keep going straight on to the NEXT bulb.
Circuit-C is a series circuit. There's only one road that electrons can take to get from one battery terminal to the other one. There's no point in the circuit where an electron has to decide which path to take.
Circuit-D is called a "series-parallel circuit", because it has characteristics of both kinds. Devices #2 and #3 are in parallel, but Device #1 is in series with them.
Circuit-E is a parallel circuit. There are two places across the top where an electron has a choice: It can decide to take a right turn and go through the bulb OR keep going straight on to the next bulb.
