question: What contracts, causing a person's elbow to straighten?
choices.text: upper arm muscles less friction finger muscles leg muscles foot muscles individual nerve cells sensory nerve cells Two pairs
choices.label: A B C D E F G H
formatted_question: What contracts, causing a person's elbow to straighten? (A) upper arm muscles (B) less friction (C) finger muscles (D) leg muscles (E) foot muscles (F) individual nerve cells (G) sensory nerve cells (H) Two pairs