The correct answer is D. Ampere-hour and watt-hour meters.
An ammeter is an instrument used to measure electric current in a circuit. A voltmeter is an instrument used to measure electric potential difference (voltage) between two points in a circuit. A wattmeter is an instrument used to measure electric power in a circuit.
An ampere-hour meter is an instrument used to measure the total electric charge that has passed through a circuit in a given time. A watt-hour meter is an instrument used to measure the total electric energy that has been used by a circuit in a given time.
Both ampere-hour and watt-hour meters are integrating instruments because they measure the total amount of something (electric charge or electric energy) that has passed through a circuit in a given time.