Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: 
Some of these pennies are shiny and copper colored. That’s how pennies look when they are new. The older pennies are dull and brown. Copper at the surface of these pennies has combined with air to become a different substance with different properties. The change in color shows that a chemical change has occurred.


Question: What type of change has occurred when a copper penny changes color?
chemical change
Chemical change.