Question: who contributed to the discovery of dna structure
[{'answer': 'Erwin Chargaff', 'provenance': [{'wikipedia_id': '235517', 'title': 'Erwin Chargaff', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 14, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '235517', 'title': 'Erwin Chargaff', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 346, 'bleu_score': 0.916705652864192, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7680766387299475224}, 'section': 'Section::::Abstract.'}]}]