Question: what was the main source of labor in the portuguese colony
[{'answer': 'Slaves', 'provenance': [{'wikipedia_id': '269408', 'title': 'Colonial Brazil', 'start_paragraph_id': 2, 'start_character': 303, 'end_paragraph_id': 2, 'end_character': 309, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '269408', 'title': 'Colonial Brazil', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 469, 'bleu_score': 0.6005921936367681, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14288071122747826990}, 'section': 'Section::::Abstract.'}]}]