Which of the following statements about chemical equations is(are) true?

a. When balancing a chemical equation, you can never change the coefficient in front of any chemical formula.

b. The coefficients in a balanced chemical equation refer to the number of grams of reactants and products.

c. In a chemical equation, the reactants are on the right and the products are on the left.

d. When balancing a chemical equation, you can never change the subscripts of any chemical formula.

e. In chemical reactions, matter is neither created nor destroyed so a chemical equation must have the same number of atoms on both sides of the  equation.