What do these two changes have in common?
baking a loaf of bread
cells using oxygen to break down sugar

 - Both are caused by heating.
 - Both are only physical changes.
 - Both are chemical changes.
 - Both are caused by cooling.
Step 1: Think about each change.
Baking a loaf of bread is a chemical change. The type of matter in the dough changes when it is baked. The dough turns into bread!
Cells using oxygen to break down sugar is a chemical change. When sugar is broken down, it forms carbon dioxide and water.
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 cells using oxygen to break down sugar is not.
Both are caused by cooling.
Neither change is caused by cooling.