question: What contracts, causing the elbow to straighten?
choices.text: upper arm muscles sensory nerve cells individual nerve cells Stomata closing less friction multinucleated cells vital to a good life mammary glands
choices.label: A B C D E F G H
formatted_question: What contracts, causing the elbow to straighten? (A) upper arm muscles (B) sensory nerve cells (C) individual nerve cells (D) Stomata closing (E) less friction (F) multinucleated cells (G) vital to a good life (H) mammary glands