Question: when did world war 2 become a world war
[{'answer': '1939', 'provenance': [{'wikipedia_id': '142735', 'title': 'World war', 'start_paragraph_id': 1, 'start_character': 524, 'end_paragraph_id': 1, 'end_character': 528, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '142735', 'title': 'World war', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 522, 'bleu_score': 0.6454403550191801, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1839041816673010142}, 'section': 'Section::::Abstract.'}]}]