If the inner lining of the air sacs neither thin nor highly vascularized, then it can be inferred that AIR SACS ARE CANNOT BE THE SITES OF GASEOUS EXCHANGE BETWEEN AIR AND BLOOD. Air sacs are generally lined with mucus and surrounded with blood capillaries.
In case of birds, air sacs play an important role in respiratory system.
I don’t know sorry but you can search on google or safari and see for icivics and it would help you
Answer:
A) climate change...........
To calculate the population density, you will divide the population by the size of the area. Hope I helped!