This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology metabolism, Subject name: Physiology
[{'content': 'Major adrenocortical hormone in blood is: \nSelect and explain. \nA. Cortisol, B. Corticosterone, C. Aldosterone, D. Deoxy corticosterone', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans: A (Cortisol) Ref: Guyton & Hall, Synthesis and Secretion of Adrenocortical Hormones, In: Textbook of Medical Physiology, 12th ed, Philadelphia, Saunders. Elsevier 2012, p 924Explanation: (See table below)', 'role': 'assistant'}]