Question: when did south africa became a member of the commonwealth
[{'answer': '1931'}, {'provenance': [{'wikipedia_id': '15755009', 'title': 'Member states of the Commonwealth of Nations', 'start_paragraph_id': 4, 'start_character': 129, 'end_paragraph_id': 4, 'end_character': 826, 'bleu_score': 0.836028594006166, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 5312785547449565197}, 'section': 'Section::::Abstract.'}]}]