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Given a scientific passage and an answer, generate a question for the given answer.

Passage: Think of a continent, like North America. Surrounding the continent are continental margins . Continental crust grades into oceanic crust at continental margins. Continental margins are under water. Almost all of North America sits on the North American Plate ( Figure below ). Both sides of the continent have continental margins, but each is very different. One continental margin of North America is an active margin. The other is a passive margin. Can you guess which is which?. Answer: oceanic crust
Output:
What does continental crust grade into at continental margins?