Question: what is the primary fuel that would be used in fusion reactors
[{'answer': 'hydrogen isotopes', 'provenance': [{'wikipedia_id': '55017', 'title': 'Fusion power', 'start_paragraph_id': 3, 'start_character': 30, 'end_paragraph_id': 3, 'end_character': 47, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]