Final answer:
A regulator with a conventional alternate-air-source second stage is widely used and well-understood, offering a reliable backup breathing source for divers in case of an emergency.
Step-by-step explanation:
Regarding the question: A regulator equipped with a conventional alternate-air-source second stage: Is this among the most widely used and readily understood type of alternate air source? The answer is True. These alternate-air-source regulators are indeed widely used and known for being straightforward and reliable, which contributes to their understanding and popularity among divers. They are designed to ensure that in the event of a primary regulator failure or air depletion, a diver can still access a breathable gas supply, either by sharing with a buddy or using the alternate air source provided by this second-stage regulator.