Question: where does the energy stored in fossil fuels come from
[{'answer': 'combustion', 'provenance': [{'wikipedia_id': '1560443', 'title': 'Fossil fuel power station', 'start_paragraph_id': 1, 'start_character': 207, 'end_paragraph_id': 1, 'end_character': 217, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]