Select the best definition of Diabetic ketoacidosis.

A. Hyperglycaemia with ketonaemia and metabolic acidosis due to severe insulin deficiency. B. Glomerular inflammation causing haematuria, reduced filtration and often hypertension. C. Obstruction of pulmonary arteries, commonly by thrombus originating in deep veins. D. Acute infection of the meninges requiring urgent antimicrobial treatment.