Which best describes the law of conservation of mass?

a: the coefficients in front of the chemicals in the reactants should be based on the physical state of the products.
b: products in the form of gasses are not considered a part of the total mass change from reactants to products.
c: when reactants contain both a solid and a liquid, the solid counts toward the overall mass and the liquid does not.
d: the mass of the reactants and products is equal and is not dependent on the physical state of the substances.