Question: what are the different types of nitrogenous bases in dna
[{'answer': 'adenine', 'provenance': [{'wikipedia_id': '1393654', 'title': 'Nitrogenous base', 'start_paragraph_id': 4, 'start_character': 393, 'end_paragraph_id': 4, 'end_character': 400, 'bleu_score': 1.0, 'section': 'Section::::Role in nucleic acids.\n'}]}, {'answer': 'guanine', 'provenance': [{'wikipedia_id': '1393654', 'title': 'Nitrogenous base', 'start_paragraph_id': 4, 'start_character': 418, 'end_paragraph_id': 4, 'end_character': 425, 'bleu_score': 1.0, 'section': 'Section::::Role in nucleic acids.\n'}]}, {'answer': 'thymine', 'provenance': [{'wikipedia_id': '1393654', 'title': 'Nitrogenous base', 'start_paragraph_id': 4, 'start_character': 431, 'end_paragraph_id': 4, 'end_character': 438, 'bleu_score': 1.0, 'section': 'Section::::Role in nucleic acids.\n'}]}, {'answer': 'cytosine', 'provenance': [{'wikipedia_id': '1393654', 'title': 'Nitrogenous base', 'start_paragraph_id': 4, 'start_character': 448, 'end_paragraph_id': 4, 'end_character': 456, 'bleu_score': 1.0, 'section': 'Section::::Role in nucleic acids.\n'}]}, {'provenance': [{'wikipedia_id': '1393654', 'title': 'Nitrogenous base', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 975, 'bleu_score': 0.7797491971080791, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 5543287996992234928}, 'section': 'Section::::Role in nucleic acids.\n'}]}]