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

Passage: Bears get their energy from their food. Brown bears eat a varied diet, from nuts and berries to fish and other animals. When bears eat a berry, they are obtaining energy that the plant originally captured from the sun. Even when a bear eats another animal, the energy in that animal ultimately came from eating a producer that captured the sun's energy. Answer: sun
Output:
Which is the ultimate energy source in a bear's food chain?