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Petoskey stones are actually fossils! They are the remains of colonial coral that lived in Lake Michigan over 350 million years ago. Their white, circular patterns outline the ancient animals contained within them.

Why did the author use a definition pattern in this passage?

to discuss different types of Petoskey stones
to present the author’s opinion of Petoskey stones
to clarify why the author decided to write about Petoskey stones
to explain what a Petoskey stone is by providing a detailed description