Gas exchange of oxygen and carbon dioxide takes place in the alveoli<span>. Oxygen from the inhaled air diffuses through the walls of the </span>alveoli<span> and adjacent capillaries into the red blood cells. The oxygen is then carried by the blood to the body tissues.</span>
Ecosystems mostly consist of both - abiotic and biotic factors. For that reason the answer which would properly address your question would be A - biotic and abiotic factors. Biotic factors are considered to represent the part of nature that are living and affect other organisms while abiotic factors are things which do not affect other living compounds.
Answer:
Mold fossil.
Explanation:
The clamshell shaped cavity is a mold fossil owing to the fact that the clamshell died, its body deteriorated but while it is deteriorating it is being covered by sediment. As a result when the clamshell completely disappears it will leave an impression on the sediment, in other words, it is a mold of the prehistoric clamshell.
