What type of vent serves two or more traps and extends from the highest fixture connection to the vent stack?

The correct answer is that the type of vent serving two or more traps and extending from the highest fixture connection to the vent stack is a circuit vent. A circuit vent is designed to serve multiple fixtures that are grouped together; it allows for the effective ventilation of the drainage system while also providing a pathway for incoming air, which helps maintain proper drainage by preventing siphoning of traps. This is particularly useful in situations where fixtures are closely aligned, as the circuit vent can extend from the high fixture to the vent stack without interruption, ensuring that all the fixtures it serves are effectively vented.

Understanding the function of a circuit vent is essential in plumbing design and code compliance, as it contributes to efficient drainage and minimizes the potential for trap seal loss. Other types of vents mentioned, such as common vents or combination waste and vent systems, serve different purposes and configurations within plumbing systems, emphasizing the tailored nature of venting solutions based on installation requirements and local codes.