Final answer:
A hood is a respiratory inlet covering that completely covers the head and neck, and may also cover portions of the shoulders and torso. It acts as a protective barrier for the respiratory system.
Step-by-step explanation:
A hood is a respiratory inlet covering that completely covers the head and neck, and may also cover portions of the shoulders and torso (option a: Hood). For example, in firefighting, firefighters wear a Nomex hood on top of their face mask and helmet to protect the unprotected areas from the intense heat of the fire. This hood acts as a protective barrier between the respiratory system and the external environment.