Question: when was chlorine gas first used in ww1
[{'answer': 'before 2 January 1915', 'provenance': [{'wikipedia_id': '167578', 'title': 'Chemical weapons in World War I', 'start_paragraph_id': 11, 'start_character': 127, 'end_paragraph_id': 11, 'end_character': 148, 'bleu_score': 1.0, 'section': 'Section::::History of poison gas in World War I.:1915: Large-scale use and lethal gases.\n'}]}, {'provenance': [{'wikipedia_id': '167578', 'title': 'Chemical weapons in World War I', 'start_paragraph_id': 11, 'start_character': 21, 'end_paragraph_id': 11, 'end_character': 317, 'bleu_score': 0.8821415355185661, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14594280223076770230}, 'section': 'Section::::History of poison gas in World War I.:1915: Large-scale use and lethal gases.\n'}]}]