I think it is C but i am not completely positive.<span />
They begin to form about 3.8 billion years ago
1. electrical signals travel toward the heart. 2. signal received by the atrioventricular node. 3.signal by the nodes in the atrium. 4.the atria contracts. 5. signal transferred to the ventricles. 6. the ventricles contract.
Auditory deals with the sense of hearing and all of the choices start with a different external factor end in a logical response, however, B is the answer because it’s external factor, a siren, is the only one that involves the sense of hearing.
