This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology and Reproduction, Subject name: Physiology
[{'content': 'Which of the following is considered the active from of calcium: \nSelect and explain. \nA. Ionised calcium, B. Albumin bound calcium, C. Phosphate bound calcium, D. Protein bound calcium', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) Ionised calcium(Ref: Ganong, 25th ed/p.375)Free calcium or ionized calcium is responsible for all the important actions of calcium', 'role': 'assistant'}]