Which of the following produces the first heart sound?
the closing of the valves between the ventricles and the body
the opening of the valves between the atria and the ventricles
the closing of the valves between the atria and ventricles
the opening of the valves between the ventricles and the body

The closing of the valves between the atria and ventricles.

Explanation:

Heart sounds are defined as noises made by the beating heart and blood flow through heart. The S1 or first heart sound is generated by turbulence due to closing of two components, mitral valve and tricupsid valve.

The mitral valve and tricupsid valve are generally known as atrioventricular valves as they present between the atria and ventricles.

S1 sound is has low frequency, which is described as 'lub' and generates at the beginning of systole

Thus, the correct answer is third option.

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.