Here's a problem to solve: Mixing baking soda and vinegar makes the temperature of the solution decrease and release carbon dioxide. Which conclusion about this investigation is not valid?

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

- A: Mixing the chemicals caused them to absorb heat.
 
- B: A chemical reaction took place.
 
- C: New elements were formed.
 
- D: The procedure caused a gas to be formed.
 