A 43-year-old patient is experiencing a sudden onset of coughing, nausea, and shortness of breath.

Comprehensive and Detailed Explanation (Based on NREMT standards):

Sudden respiratory symptoms following prolonged cleaning strongly suggest chemical inhalation, particularly from cleaning agents such as ammonia or bleach. Mixing chemicals or using them in poorly ventilated areas can release toxic gases that cause coughing, nausea, and dyspnea.

Option D is correct because inhaled chemical irritants commonly cause acute respiratory distress that improves with oxygen therapy.

Option A typically causes chronic symptoms, not sudden onset.

Option B does not cause respiratory distress.

Option C does not explain the environmental exposure or oxygen response.

NREMT emphasizes recognizing environmental hazards and removing patients from the source while providing supportive care.