Due to its system of nine air sacs connected to the lungs, the respiratory system of birds is arguably the most effective respiratory system of all air-breathers. upon inhalation, air first flows into posterior air sacs, then into the lungs, and then into anterior air sacs on the way to being exhaled. thus, there is one-way flow of air through the lungs, along thousands of tubules called parabronchi. birds generate a lot of heat, especially during flight. yet the adipose tissue under their skin and the feathers atop their skin make it difficult to eliminate excess heat across the skin. which of the following alternatives can absorb body heat and eliminate it from the bird most effectively?

The correct answer is - air sacs.

Explanation:

Air sacs of birds are tiny bags or sacs of the trachea as an extra part or extension of the respiratory organ lungs in birds.

Air sacs increase the efficiency of the lungs by providing a larger surface area for the gas exchange. Air sacs are also helpful in absorbing the body heat of the birds which is not able to move out of the body due to adipose tissue. Air sacs help in eliminate body heat efficiently with the breathing process.

Thus, the correct answer is - air sacs.

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."