This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': "True statement about 'instantaneous mean vector' a) Equal & same as mean QRS vectorb) It is drawn through the centre of vector in a direction from base toward apexc) Summated vector of generated potential at particular instant caused by inflowing septal depolarizationd) When a vector is exactly horizontal and directed toward the person's left side, the vector is said to extend in the direction of 0 degrees \nSelect and explain. \nA. abc, B. acd, C. bcd, D. bd", 'role': 'user'}, {'content': 'Answer: C \nExplanation: In a normal heart, the current flows from the base towards apex. So the vector is pointed towards the apex at an angle of +59o. The angle is calculated from a vector running horizontally towards left, which is 0o. Instantaneous mean vector is the summated vector of general potential at a given instant due to septal depolarization.', 'role': 'assistant'}]