Final answer:
When a system loses energy, it is transferred to or gained by another system.
Step-by-step explanation:
When a system loses energy, the energy is not destroyed. Instead, it is transferred to another system or converted into a different form of energy. This is known as the law of conservation of energy, which states that energy cannot be created or destroyed, only transferred or transformed.
For example, when a basketball is dropped from a height, its potential energy is converted into kinetic energy as it falls to the ground. The lost potential energy is gained by the kinetic energy of the falling basketball.
So, the correct answer is D. The energy lost by the system is gained by another system.
Learn more about energy transfer