The opening and closing of the heart valves is caused by Multiple Choice action potentials within the cusps of the valves. pressure changes of alternating contraction and relaxation during the cardiac cycle. contraction and relaxation of papillary muscles that pull on heart strings. contraction of the smooth muscle in the walls of the great vessels leaving the heart.

explanation:

plz give me the characteristics.

bc blah

explanation:

bc blah

six grader is what i am ssorry

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.