The correct answer is C) diverter. A variable shunt connected across the series field coils of a DC compound wound generator is called a diverter. This allows the operator to adjust the degree of compounding by controlling the amount of current flowing through the series field coils. The diverter provides a variable resistance path in parallel with the series field, enabling the fine-tuning of the generator's output voltage. The other options are incorrect because: A) converter is a device that changes one form of electrical energy to another, B) rheostat is a variable resistor used to control current, and D) divider is a circuit that splits a signal into two or more parts.