Within the Red Hat certification program, the RHCA is considered the most complete (and grueling) certification among the seven major Red Hat certifications. In fact, some equate the prestige of the RHCA to that of the Microsoft Certified Master and possibly the CCIE.
A plumbing fixture like a sink can not function properly without a sink vent. When a drain pipe drains it creates a negative pressure in the sink drain; the negative pressure will pull the water out of the p-trap of the sink that's draining and sewer gases can enter your home if a sink vent is not installed.
Air return vents are necessary to prevent a buildup of pressure in the structure that may lead to various health problems, as well as preventing mold and mildew, and deterioration of the structure due to moisture buildup. As warm air is forced into a room, it replaces cold air already in the room.