question: what needs to be scratched to measure hardness?
choices.text: nails stoma air h2o oaks poles weater gems
choices.label: A B C D E F G H
fact2: Most gem stones are hard minerals.
combinedfact: measuring gem hardness requires scratching them
formatted_question: what needs to be scratched to measure hardness? (A) nails (B) stoma (C) air (D) h2o (E) oaks (F) poles (G) weater (H) gems