In a series circuit, the total voltage equals the sum of the

• A. Voltage source
• B. Current in each branch
• C. Sum of the voltage drops
• D. Total resistance

Answer: (C)

In a series circuit, the voltages across the components add up to the source voltage. The same current flows through every element, so each component drops a portion of the supply voltage, and when you add all those drops together you recover the total voltage provided by the source. That's why the total voltage equals the sum of the voltage drops.

The other ideas don’t fit as well: the voltage source is the cause of the voltage, not the sum of the drops; there’s only one path in a series circuit so there aren’t multiple branch currents to add; and the total resistance affects the current through Ohm’s law but isn’t the sum of voltage drops.