I believe a. is the answer
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Inhalants can be breathed in through the nose or the mouth in a variety of ways, such as—
"sniffing" or "snorting" fumes from containers;
spraying aerosols directly into the nose or mouth;
"bagging" — sniffing or inhaling fumes from substances sprayed or deposited inside a plastic or paper bag;
"huffing" from an inhalant-soaked rag stuffed in the mouth; and
inhaling from balloons filled with nitrous oxide.
