A _______________ vent terminates through the roof and allows air in and out of the drainage system; whereas a ______________ vent only allows air into the system but does not release any air or gases from the system.

The correct choice highlights the function of a primary vent and a secondary vent within an RV's drainage system. A primary vent, which extends through the roof, serves a crucial role by allowing both air and gases to escape from the drainage system into the atmosphere. This helps maintain pressure balance and prevents the buildup of harmful gases, ensuring proper drainage and ventilation.

In contrast, a secondary vent is designed to allow air into the drainage system without permitting any gases or air to exit. This is essential for maintaining the flow of wastewater and preventing any vacuum conditions that could disrupt drainage, but it does not handle gas release.

Understanding the functional differences between these types of vents is key for RV technicians as it influences how they install and maintain drainage systems in a way that ensures safety and efficiency.