Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: When a scientist performs an experiment, there are many changes that can occur. Which observation should she list as a chemical change?
A change in color, a release of gas, or the formation of a solid or liquid precipitate.