What do these two changes have in common?
a log decomposing in the woods
an old sandwich rotting in a trashcan

 - 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.
The breakdown of plant and animal matter by organisms such as fungi and earthworms is called decomposition. A log decomposing in the woods is a chemical change.
As the log breaks down, the type of matter in it changes. Over time, the log becomes softer and has a different smell.
A sandwich rotting is a chemical change. The matter in the sandwich 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.