Which option states the principle behind the law of conservation of mass and the law of conservation of energy?

the law of conservation of mass and the law of conservation of energy are fundamental principles in science and are the same - that in a closed system, neither energy nor mass can be created or destroyed. they must remain the same but can be converted from one form to another.

because einstein showed that mass n energy is the same and can be converted from one to another, the law of conservation of mass and the law of conservation of energy become the law of conservation of mass and energy.

The law of conservation of mass or principle of mass conservation states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as system mass cannot change quantity if it is not added or removed. Hence, the quantity of mass is "conserved" over time.