Question: who has won the men's single title in the australian open tennis tournament 2018
[{'answer': 'Roger Federer', 'provenance': [{'wikipedia_id': '55901829', 'title': "2018 Australian Open – Men's Singles", 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 13, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]