Which one of the following statements is correct?

a. a series circuit must contain at least two load devices.
b. a parallel circuit contains only one electrical component.
c. a series circuit must contain resistors.
d. a parallel circuit contains two or more electrical paths for current to follow.

In fact, this is the definition of a parallel circuit. The one that contains two or more electrical paths for current to follow. But what is current? current or electric current is the net flow of positive charges measured in Ampers (A). So in parallel circuits current follows two or more electrical paths. An example is shown in Figure below. As you can see, currents have been indicated in red and pass through elements E1, E2 and E3.