This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': "Einthoven's triangle, what is the value of lead III when lead I = 2 mv and Lead II = 1 mv \nSelect and explain. \nA. 1, B. 2, C. 3, D. 4", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Einthovens formula states that the sum of voltages from lead I plus those from lead III minus those from lead II is zero. Lead I+III-II=0 This is based on the principle that the sum.of the voltages in a closed path equals zero. Because the positive and negative electrodes of lead II are reversed. So it is subtracted instead of adding.', 'role': 'assistant'}]