What feature of alveoli adapts them to efficient gas exchange?
a. they have muscles which pump air in and out regularly.
b. their membranes are more permeable to gases than water.
c. a constant blood supply flows through them.
d. a dense network of capillaries surrounds them.

D is the correct answer. - A dense network of capillaries surrounds them.

Capillaries are very small about 1 cell thick which makes them more suitable to exchanging gases rather than a vein or an artery.Capillaries allow the exchange of gases, nutrients and fluids by the process of diffusion between the body and the body tissues. 

Glucose, also called grape sugar, blood sugar or corn sugar, is among the simplest and one of the primary naturally occurring sugars. produced naturally by plants as the primary photosynthesis product, it is heavily used by living beings as a main energy source and is necessary for cellular respiration. chemically, it is a monosaccharide carbohydrate and serves as a building block for complex sugars like starch.