Induction cup relay is operated due to changes in

The induction cup relay operates based on the principle of electromagnetic induction, which produces torque in the relay mechanism.

Current: Changes in current generate a magnetic field, influencing the operation of the relay.

Voltage: Variations in voltage also affect the electromagnetic field and contribute to the relay's operation.

Impedance: As impedance changes, it alters the relationship between current and voltage, impacting the electromagnetic torque and thus the relay's activation.

Since the relay responds to changes in current, voltage, and impedance, all of the above factors contribute to its operation.

Therefore, Option D is the correct answer.