Question: what is the diameter of earth in km
[{'answer': 'about 12,742 km'}, {'provenance': [{'wikipedia_id': '9228', 'title': 'Earth', 'start_paragraph_id': 79, 'start_character': 0, 'end_paragraph_id': 79, 'end_character': 615, 'bleu_score': 0.783946994981626, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 764602865629853680}, 'section': 'Section::::Orbit and rotation.:Orbit.\n'}]}]