Which structure of the respiratory system plays the main role in carry out the system’s primary function?
trachea
pharynx
alveoli
nose

alveoli

Explanation:

Alveoli are the basic functional units of respiratory system which play actual role of exchange of gases. Alveoli are tiny balloon like air sacs which exist as a single cell not as a group of cells. They are responsible for exchange of gases like oxygen and carbon dioxide in our body. As soon as we inhale with the help of nose, a lot of air full of oxygen first reaches pharynx and then trachea. From trachea it ultimately reaches alveoli. Since alveoli have air full of oxygen so the partial pressure is more at alveolar end while capillaries nearby alveoli have blood which is full of carbon dioxide so the partial pressure of carbon dioxide is more in capillaries. Now, a gradient is set up as a result of which alveoli and blood capillaries exchange oxygen and carbon dioxide passively. Oxygen molecules from alveoli tend to diffuse to capillaries while carbon dioxide molecules from capillaries tend to move towards alveoli. The movement/exchange of gases continues until an equilibrium condition is reached. After which the carbon dioxide is exhaled out of out body with the help of same respiratory tract mentioned above.

the two answers are a, the population of birds with large beaks will increase on the island, and c, the trait for large beaks will be passed on to future generations through natural selection. the reason for that is because if the birds that have beaks developed for eating small seeds lose all of their food, they will go hungry and eventually starve because they physically cannot eat the large seeds, therefore making the population of large beaked birds higher. also, if the trait of large beaks are dominant on the island over small beaks, then over time the large beaked birds will reproduce more and more, while the smaller beaked birds will reproduce less and less because they can't survive with the food provided. that leads to the trait of small beaks disappearing and the trait of large beaks taking over the island.