question: Commands to the muscles are sent by what?
choices.text: Muscles in the upper arm. animals in Class Aves through the skin progesterone hydraulic forces radio waves electrical impulses velocity and intent
choices.label: A B C D E F G H
formatted_question: Commands to the muscles are sent by what? (A) Muscles in the upper arm. (B) animals in Class Aves (C) through the skin (D) progesterone (E) hydraulic forces (F) radio waves (G) electrical impulses (H) velocity and intent