Question: when did the triplets join the return of superman
[{'answer': 'July 6', 'provenance': [{'wikipedia_id': '42673797', 'title': 'The Return of Superman (TV series)', 'start_paragraph_id': 19, 'start_character': 154, 'end_paragraph_id': 19, 'end_character': 160, 'bleu_score': 1.0, 'section': 'Section::::Cast.:Cast history.\n'}]}, {'provenance': [{'wikipedia_id': '42673797', 'title': 'The Return of Superman (TV series)', 'start_paragraph_id': 19, 'start_character': 0, 'end_paragraph_id': 19, 'end_character': 160, 'bleu_score': 0.9321022168949711, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16517974117616473482}, 'section': 'Section::::Cast.:Cast history.\n'}]}]