Question: how many u s senators are up for reelection in 2018
[{'answer': '33 of the 100 seats', 'provenance': [{'wikipedia_id': '38680975', 'title': '2018 United States Senate elections', 'start_paragraph_id': 1, 'start_character': 71, 'end_paragraph_id': 1, 'end_character': 90, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]