The correct answer is A (438 cubic feet), representing air breathed in 24 hours. At rest, humans breathe about 6-7 liters per minute; over 24 hours, this totals approximately 8,500-10,000 liters or 300-350 cubic feet. 438 cubic feet is plausible for an active day. Options B (435), C (436), and D (448) are very close values making this a precise numerical distinction.