Question: which rock unit on the surface of the moon is the youngest
[{'answer': 'mare basalts', 'provenance': [{'wikipedia_id': '2096232', 'title': 'Geology of the Moon', 'start_paragraph_id': 23, 'start_character': 16, 'end_paragraph_id': 23, 'end_character': 28, 'bleu_score': 1.0, 'section': 'Section::::Lunar landscape.:Maria.\n'}]}, {'provenance': [{'wikipedia_id': '2096232', 'title': 'Geology of the Moon', 'start_paragraph_id': 23, 'start_character': 0, 'end_paragraph_id': 23, 'end_character': 576, 'bleu_score': 0.979054689945215, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4618605001339632967}, 'section': 'Section::::Lunar landscape.:Maria.\n'}]}]