What is necessary to measure the hardness of materials?
treatment tapping rubbing tasting lamphreys scratching strength potassium
A B C D E F G H
Travel is required as necessary.
To measure the hardness of materials, scratching those materials is necessary.
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