What do these two changes have in common?
a piece of avocado turning brown
a piece of pizza rotting in a trashcan

 - Both are only physical changes.
 - Both are chemical changes.
 - Both are caused by heating.
 - Both are caused by cooling.
Step 1: Think about each change.
A piece of avocado turning brown is a chemical change. The avocado reacts with oxygen in the air to form a different type of matter.
If you scrape off the brown part of the avocado, the inside will still be green. The inside hasn't touched the air. So the chemical change hasn't happened to that part of the avocado.
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.