What do these two changes have in common?
a piece of pizza rotting in a trashcan
burning a marshmallow over a campfire

 - Both are chemical changes.
 - Both are caused by cooling.
 - Both are caused by heating.
 - Both are only physical changes.
Step 1: Think about each change.
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.
Burning a marshmallow is a chemical change. The heat from the fire causes the type of matter in the marshmallow to change. The marshmallow becomes black and crispy.
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.
Burning is caused by heating. But a piece of pizza rotting is not.
Both are caused by cooling.
Neither change is caused by cooling.