When the ventricles contract, the valve prevents blood flow from the: A ventricle to atrium
B atrium to ventricle
C left ventricle to the right ventricle
D right atrium to the left atrium

The answer is A i think

The proton has a positive charge while the neutron has no charge they both make up the nucleus of the atom while the elections have a negative charge and surround the nucleus of the atom. the protons and electrons are used to calculate the atom's mass whereas the neutrons don't affect the mass