What do these two changes have in common?
baking cookies
a piece of pizza rotting in a trashcan

 - Both are caused by heating.
 - Both are chemical changes.
 - Both are caused by cooling.
 - Both are only physical changes.
Step 1: Think about each change.
Baking cookies is a chemical change. The type of matter in the cookie dough changes when it is baked. The cookie dough turns into cookies!
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.
Baking is caused by heating. But a piece of pizza rotting is not.
Both are caused by cooling.
Neither change is caused by cooling.