Question: any substance that can provoke an immune response is an
[{'answer': 'antigen', 'provenance': [{'wikipedia_id': '1915', 'title': 'Antigen', 'start_paragraph_id': 1, 'start_character': 15, 'end_paragraph_id': 1, 'end_character': 22, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]