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

the more fit you are, the faster the recovery. your heart rate drops most sharply in the first minute after you stop exercising; it should then fall about 20 beats a minute—a drop of less than 12 beats a minute is considered abnormal. this “recovery heart rate” is measured as part of an exercise stress test.

the answer is shoe size