Question: what are the 4 types of nitrogenous bases
[{'answer': 'adenine ( A )', 'provenance': [{'wikipedia_id': '1393654', 'title': 'Nitrogenous base', 'start_paragraph_id': 4, 'start_character': 393, 'end_paragraph_id': 4, 'end_character': 405, 'bleu_score': 1.0, 'section': 'Section::::Role in nucleic acids.\n'}]}, {'answer': 'uracil ( U )', 'provenance': [{'wikipedia_id': '1393654', 'title': 'Nitrogenous base', 'start_paragraph_id': 4, 'start_character': 406, 'end_paragraph_id': 4, 'end_character': 417, 'bleu_score': 1.0, 'section': 'Section::::Role in nucleic acids.\n'}]}, {'answer': 'guanine ( G )', 'provenance': [{'wikipedia_id': '1393654', 'title': 'Nitrogenous base', 'start_paragraph_id': 4, 'start_character': 418, 'end_paragraph_id': 4, 'end_character': 430, 'bleu_score': 1.0, 'section': 'Section::::Role in nucleic acids.\n'}]}, {'answer': 'thymine ( T )', 'provenance': [{'wikipedia_id': '1393654', 'title': 'Nitrogenous base', 'start_paragraph_id': 4, 'start_character': 431, 'end_paragraph_id': 4, 'end_character': 443, 'bleu_score': 1.0, 'section': 'Section::::Role in nucleic acids.\n'}]}, {'answer': 'cytosine ( C )', 'provenance': [{'wikipedia_id': '1393654', 'title': 'Nitrogenous base', 'start_paragraph_id': 4, 'start_character': 448, 'end_paragraph_id': 4, 'end_character': 461, 'bleu_score': 1.0, 'section': 'Section::::Role in nucleic acids.\n'}]}, {'provenance': [{'wikipedia_id': '1393654', 'title': 'Nitrogenous base', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 0, 'bleu_score': 1.0, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4507739985872130053}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '1393654', 'title': 'Nitrogenous base', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 972, 'bleu_score': 0.7524747065693961, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4507739985872130053}, 'section': 'Section::::Role in nucleic acids.\n'}]}, {'provenance': [{'wikipedia_id': '1393654', 'title': 'Nitrogenous base', 'section': 'Section::::Role in nucleic acids.\n', 'start_paragraph_id': 4, 'end_paragraph_id': 4, 'meta': {'evidence_span': ['These nitrogenous bases are adenine (A), uracil (U), guanine (G), thymine (T), and cytosine (C).', 'adenine (A), uracil (U), guanine (G), thymine (T), and cytosine (C)', 'These nitrogenous bases are adenine (A), uracil (U), guanine (G), thymine (T), and cytosine (C).']}}]}]