Question: when were the first trenches dug in ww1
[{'answer': 'by the start of WWI', 'provenance': [{'wikipedia_id': '182259', 'title': 'Trench warfare', 'start_paragraph_id': 27, 'start_character': 64, 'end_paragraph_id': 27, 'end_character': 83, 'bleu_score': 1.0, 'section': 'Section::::World War I: Entrenchment.:Implementation.\n'}]}, {'provenance': [{'wikipedia_id': '182259', 'title': 'Trench warfare', 'start_paragraph_id': 27, 'start_character': 0, 'end_paragraph_id': 27, 'end_character': 578, 'bleu_score': 0.980097014099621, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3325067157272868937}, 'section': 'Section::::World War I: Entrenchment.:Implementation.\n'}]}]