What do these two changes have in common?
plants making food from sunlight, air, and water
a piece of pizza rotting in a trashcan

 - Both are chemical changes.
 - Both are caused by heating.
 - Both are caused by cooling.
 - Both are only physical changes.
Step 1: Think about each change.
Plants making food is a chemical change. Plants use energy from sunlight to change air and water into food. The food is sugar. Sugar is a different type of matter than air or water.
A piece of pizza rotting is a chemical change. The matter in the pizza breaks down and slowly turns into a different type of matter.
Step 2: Look at each answer choice.
Both are only physical changes.
Both changes are chemical changes. They are not physical changes.
Both are chemical changes.
Both changes are chemical changes. The type of matter before and after each change is different.
Both are caused by heating.
Neither change is caused by heating.
Both are caused by cooling.
Neither change is caused by cooling.