question: Which of the following is a correctly written chemical equation that demonstrates the conservation of mass?
choices.text: Mg + HCl -> H_{2} + MgCl_{2} H_{2}O + CO_{2} -> H_{2}CO_{3} KClO_{3} -> KCl + O_{2} H_{2} + O_{2} -> H_{2}O
choices.label: A B C D