HELP!! Which features of alveoli enable them to exchange gases efficiently? (Select all that apply.)

A. thin walls

B. surrounded by blood vessels

C. small numbers of them in each lung

D. large surface area

Do not scam me using links or attachments (except photos of the answer) or answer this by saying a simple yes or no because that also scams me.

Johnny rode his bike to a friend's house 4 blocks down the street in his neighborhood. he immediately rode back home once he realized his friend was not able to play. what was his displacement for the total bike ride? how did you determine this? what could we use as a reference point to determine he was in motion during his bike ride? why can you use it as a reference point

Construct at least two possible hypotheses for the student’s experiment.

The smallest parts of these that retain their original properties are called