What do these two changes have in common?
milk going sour
a copper statue turning green

 - Both are caused by cooling.
 - Both are only physical changes.
 - Both are chemical changes.
 - Both are caused by heating.
Step 1: Think about each change.
Milk going sour is a chemical change. The type of matter in the milk slowly changes. The new matter that is formed gives the milk its sour taste.
A copper statue turning green is a chemical change. The copper reacts with oxygen in the air. This reaction forms a different type of matter called copper oxide. The copper oxide is green.
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.