Standardized exams, for instance National Medical Boards or specialty board certification for me, have questions on the test for validation purposes, that count only on later tests, after being validated. Questions that fail validation, are eliminated. Grading on the curve helps adjust for the degree of difficulty of the exam and/or for problem questions. As an undergraduate, I served as a teaching assistant for several classes. Very occasionally, a question would simply be eliminated in the scoring because of a problem with it, rather than adjusting the scoring after the fact.
The author of this question had a specific definition in mind for "extra supply of air", that many of us interpreted differently. This point appears to have been known to the author, as this entirely determines whether one chooses a or d as the correct answer. If c would have read, "releases additional gas from your supply", it would change things.
Writing good questions is not always easy. I wrote test questions for the lectures I delivered to medical school students for many years. Students occasionally challenged questions and revealed something that I was unaware of when I wrote it. I wrote better questions with experience.