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

the answer is down feathers. Or C

Explanation:

I just took the unit review test

the transfer of energy between two molecules spaced just nanometers apart plays a key role in many technologies, including photovoltaics, quantum information systems, lighting, and sensors, as well as in biophysics to measure nanometer distances and in photosynthesis. but an open question in this area is what effect, if any, the surrounding photonic environment has on this nanoscale energy transfer. by designing and performing a carefully controlled experiment to answer this question, scientists have settled the debate and found clues to improving the efficiency of many of the technologies that rely on this process.

explanation:

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.