A
not every expirement has control
I believe c is the right answer.
english:
In physics and chemistry, the law of conservation of energy states that the total energy of an isolated system remains constant; it is said to be conserved over time.
spanish:
En física y química, la ley de conservación de la energía establece que la energía total de un sistema aislado permanece constante; se dice que se conserva con el tiempo.