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.
RrTt ....means brown leaves and tall stems !
so answer is D !
The consequence of over fertilization can include eutrophication in nearby waters.
hope it helps u.......
D because no human has the ability to make their own food within themselves.