Which is an adaptation that birds maintain a stable body temperature? air sacs connected to lungs large chest muscles down feathers nearly hollow bones

Hey there!

Here is your

The proper answer to this question is option A "air sacs connected to lungs". 

Reason:

Air sacs are used for birds to breath through in order to have air go to the lungs allowing the body to remain a steady (stable) temperature. Which means air sacs would be the answer.

Also...

Its not option B because large chest muscles would probably allow the bird to carry bigger foods such as: larger worms. Its not down feathers because down feathers are used to keep the bird warm its used in: jacket's, sleeping bags, etc... (anything the will help keep your body warm. Down fathers are in only a few types of birds mainly babies and its a thermal insulator. Its also not option D because hollow bones are mainly used for the bird to fly more easier its like less weight for the bird.

Therefore the answer is A.

If you need anymore help feel free to ask me!

Hope this helps!

~Nonportirt