Here's a problem to solve: When frozen carbon dioxide (CO_{2}) is heated, it changes directly into a gas. Which statement best indicates that a physical change has taken place?

Among the 4 following options, which is the correct answer?

- A: Heat caused an increase in gas production.
 
- B: Heat caused a new substance to form.
 
- C: Heat caused a decrease in energy.
 
- D: Heat caused a change in state.
 