When listening to a beating heart, if a physician hears two “lub” sounds instead of one, which of the following is true?
1.The semilunar valves are not closing simultaneously.
2.The atrial blood is flowing backward, causing the extra sound.
3.The atrioventricular (AV) valves are not closing at the same time.
4.The AV and semilunar valves are not closing at the same time.
5.No such sound has ever been heard.
3
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