question: What is necessary to measure the hardness of materials?
choices.text: treatment tapping rubbing tasting lamphreys scratching strength potassium
choices.label: A B C D E F G H
fact2: Travel is required as necessary.
combinedfact: To measure the hardness of materials, scratching those materials is necessary.
formatted_question: What is necessary to measure the hardness of materials? (A) treatment (B) tapping (C) rubbing (D) tasting (E) lamphreys (F) scratching (G) strength (H) potassium