The correct answer is C. impedance relays.
Distance relays are used to protect power systems against faults that occur outside the protected zone. They work by measuring the impedance between the relay and the fault location. The impedance is a measure of the opposition to the flow of current. Distance relays are typically used to protect transmission lines, but they can also be used to protect transformers and other equipment.
Split-phase relays are used to protect motors against phase imbalance. They work by measuring the voltage and current in each phase of the motor. If the voltage or current in one phase is significantly different from the voltage or current in the other phases, the relay will trip.
Reactance relays are used to protect power systems against faults that occur on lines with high reactance. They work by measuring the reactance between the relay and the fault location. The reactance is a measure of the opposition to the flow of current due to inductance. Reactance relays are typically used to protect long transmission lines.
None of the above is not a correct answer.