Question: earth's crust under oceanic is composed of this rock type
[{'answer': 'mafic rocks , or sima', 'provenance': [{'wikipedia_id': '981252', 'title': 'Oceanic crust', 'start_paragraph_id': 2, 'start_character': 39, 'end_paragraph_id': 2, 'end_character': 60, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '981252', 'title': 'Oceanic crust', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 362, 'bleu_score': 0.798726809513276, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 773431157683047992}, 'section': 'Section::::Abstract.'}]}]