Question: invar tapes are made of an alloy of
[{'answer': 'nickel -- iron'}, {'provenance': [{'wikipedia_id': '544888', 'title': 'Invar', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 291, 'bleu_score': 0.957870874785216, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 12030626502068323367}, 'section': 'Section::::Abstract.'}]}]