The lavatories displayed are _________ vented.

The correct choice indicates that the lavatories are vented as a common system. In plumbing, common venting involves connecting multiple fixtures to a single vent system, which helps in maintaining air pressure in the drainage system and allows sewer gases to escape safely. This approach is efficient, particularly in areas where multiple fixtures are grouped closely together, reducing the amount of vent piping needed and simplifying the overall installation.

Common venting also ensures that the fixtures share the same vent path, which can be beneficial in maintaining proper drainage and reducing the risk of trap siphoning. While individually vented fixtures have their vents, the common vent system promotes better airflow and less obstruction compared to using separate vents for each fixture. This is particularly important in residential and commercial plumbing designs where space and resource efficiency are considerations.

The other options, while they describe various venting methods, do not apply to the described scenario. Individual venting would mean each lavatory has its vent, which increases complexity and material use. Openly vented systems are not a standard term in plumbing and may create confusion regarding proper venting practices. Exhaust venting is more commonly associated with HVAC systems rather than plumbing, focused on removing air or gases rather than preventing siphoning in drainage systems.