In a teaching session, Asthma is correctly explained as:

A. A clinical spectrum caused by acute myocardial ischaemia, including unstable angina and myocardial infarction. B. A rapid severe systemic hypersensitivity reaction that may compromise airway, breathing or circulation. C. A supraventricular arrhythmia with disorganised atrial activity and an irregularly irregular pulse. D. A chronic inflammatory airway disorder with variable and usually reversible airflow obstruction.