What do these two changes have in common?
a piece of avocado turning brown
burning a marshmallow over a campfire

 - Both are only physical changes.
 - Both are caused by cooling.
 - Both are chemical changes.
 - Both are caused by heating.
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.
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 avocado turning brown is not.
Both are caused by cooling.
Neither change is caused by cooling.