Question: when was the eiffel tower built and why
[{'answer': 'Constructed from 1887 -- 1889'}, {'answer': "the entrance to the 1889 World 's Fair"}, {'provenance': [{'wikipedia_id': '9232', 'title': 'Eiffel Tower', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 383, 'bleu_score': 0.9112141177075951, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7192885310655808428}, 'section': 'Section::::Abstract.'}]}]