What do warm up and cool down have in common

The lower respiratory system includes the a. lungs. b. esophogus. c. larynx. d. pharynx

Astructural difference between the trachea and esophagus that prevents the trachea from collapsing is the presence of: a) smooth muscle b) skeletal muscle c) respiratory cilia d) rings of cartilage

What is the hormone in your brain that makes you feel happy?