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
Closing  of  the  mitral  valve  begins  at point: 
Select and explain. 
A. A, B. B, C. C, D. D
A: A
Answer: A: A 
Explanation: At point D, the pressure within the left ventricle is less than the pressure in the left atrium, and, therefore, the mitral valve opens and ventricular ﬁlling begins. At point A, the ventricle begins to contract, raising its pressure above that in the atrium and closing the mitral valve. The aortic valve opens at point B and closes at point C.