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

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.

answer:

convection currents in the magma drive plate tectonics. heat generated from the radioactive decay of elements deep in the interior of the earth creates magma (molten rock) in the aesthenosphere. the aesthenosphere (70 ~ 250 km) is part of the mantle, the middle sphere of the earth that extends to 2900 km.