Heat is added to a substance, but its temperature does not rise. Which one of the following statements provides the best explanation for this observation? The substance must be cooler than its environment. The substance undergoes a change of phase. The substance has unusual thermal properties. The substance must be a gas. O The substance must be a non-perfect solid.

Heat is added to a substance, but its temperature does not rise. Which one of the following statements provides the best explanation for this observation? The substance must be cooler than its environment. The substance undergoes a change of phase. The substance has unusual thermal properties. The substance must be a gas. O The substance must be a non-perfect solid.