Question: when did the first grass appear on earth
[{'answer': 'around 40 million years ago'}, {'provenance': [{'wikipedia_id': '11008314', 'title': 'Evolutionary history of plants', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 665, 'bleu_score': 0.5066477438472611, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4350446562770404912}, 'section': 'Section::::Abstract.'}]}]