Final answer:
When temperature decreases in a system, it can cause a liquid to become a solid, due to a reduction in particle movement and kinetic energy, resulting in freezing.
Step-by-step explanation:
Temperature is a measure of the average kinetic energy of the particles in a substance, and it plays a crucial role in the phase changes of matter. When the temperature of a system decreases, the particles in the system move slower, and their average kinetic energy drops. This can lead to a state change in which a liquid becomes a solid. This is known as freezing, and it is due to the decrease in temperature causing the intermolecular forces to dominate over the kinetic energy of the particles, forcing them into a fixed position typical of a solid state.
Based on the provided choices, the correct answer to the question of what can occur if the temperature decreases in a system is 'D. A liquid becomes a solid.'