Answer:
1. D. Burning Coal and Natural Gas
2. D. Larger; Louder
3. D. It has a lower pitch and is quieter than the first note.
Explanation:
Not 100% certain of number 3, but I'm pretty certain it is correct. 1 and 2 are for sure correct.
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.
A theory in science is a remark on what happened
