How is air supplied to an HVAC unit?

The correct choice identifies that air is supplied to an HVAC unit through a grille, which serves as an entry point that allows conditioned air to flow into the system. Grilles are often equipped with filters to help clean the air before it is circulated, making them essential components in ensuring the efficiency and effectiveness of the HVAC system.

Grilles can also help direct airflow and are often found in areas where ventilation is needed, thus playing a key role in the overall function of the HVAC unit. It's important to understand that while ducts are used to transport air within the system and various outlets help deliver air to specific areas, the actual entry point into the unit is often through a grille that manages the airflow more directly.