Why are all the people on earth members of the same biological sprecies?

Its simple evolutionary biology; we all evolved seperate from a primate species. if you go back in the tree of life you can find where chimps and humans split off from a common accestor. 

The answer would be a (carbohydrates)

Air goes past the epiglottis and into the trachea when you breathe in. from there, it goes to your vocal cords in the larynx until it reaches the bronchi. from the bronchi, air passes into each lung.