What distinguishes a series circuit from a parallel circuit?

In a series circuit, components are connected end-to-end, forming a single path for current flow. This characteristic is fundamental to series circuits, as it means that the same current flows through each component in the circuit. When the components are arranged this way, the circuit's total resistance is simply the sum of the individual resistances. This connection also results in a voltage drop across each component based on its resistance, but the key point is that all components are aligned in such a manner that they form a chain or series, as one follows the other directly.

The other options mention aspects that do not accurately describe how series circuits work. For example, in series circuits, voltage drops are not equal across each component (which would happen in a parallel circuit). Therefore, the defining feature of a series circuit is its end-to-end configuration, creating a single path for current to take.