According to the law of conservation of energy which statement must be true?

D. The total energy of a system can increase only if energy enters the system

Explanation:

The law of conservation of energy states that, in a closed system, energy can't be created, and can't be destroyed, but can however be transformed or converted from one form of to another, i.e. chemical energy to heat energy. According to this law, the total energy in the system remains the same, as energy being used is just simply a transformation of one energy to another rather than the actual creation of destruction of energy.

Therefore, the statement about this law that must be true considering the given options is: "The total energy of a system can increase only if energy enters the system."