Question: who gave the concept of elasticity of demand
[{'answer': 'Alfred Marshall', 'provenance': [{'wikipedia_id': '216353', 'title': 'Price elasticity of demand', 'start_paragraph_id': 26, 'start_character': 67, 'end_paragraph_id': 26, 'end_character': 82, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'provenance': [{'wikipedia_id': '216353', 'title': 'Price elasticity of demand', 'start_paragraph_id': 26, 'start_character': 277, 'end_paragraph_id': 26, 'end_character': 1327, 'bleu_score': 0.8446244035395101, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 6266430930751102172}, 'section': 'Section::::History.\n'}]}]