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
According to Einthoven's law: 
Select and explain. 
A. 1+2=3, B. 1+3=2, C. 2+3=1, D. 1+2+3=0
B: 1+3=2
Answer: B: 1+3=2 
Explanation: The sum of the voltages in lead 1&3 equals the voltage in lead 2, mathematically this principle is called as Einthoven law.
Einthoven’s Law:
Einthoven’s law states that if the ECGs are recorded simultaneously with the three limb leads, the sum of the potentials recorded in leads I and III will equal the potential in lead II.