Question: when did the cross become a christian symbol
[{'answer': 'in the 2nd century', 'provenance': [{'wikipedia_id': '27484195', 'title': 'Christian cross', 'start_paragraph_id': 8, 'start_character': 65, 'end_paragraph_id': 8, 'end_character': 83, 'bleu_score': 1.0, 'section': 'Section::::History.:Early Christian usage.\n'}]}, {'provenance': [{'wikipedia_id': '27484195', 'title': 'Christian cross', 'start_paragraph_id': 8, 'start_character': 0, 'end_paragraph_id': 8, 'end_character': 1225, 'bleu_score': 0.9382875397013821, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10544494526313107227}, 'section': 'Section::::History.:Early Christian usage.\n'}]}]