I believe it’s a chromosome.
"The red blood cell<span> survives on average only 120 days. </span>Red cells<span> contain a special protein called hemoglobin, which helps carry oxygen from the lungs to the rest of the </span>body<span> and then returns carbon dioxide from the </span>body<span> to the lungs so it can be exhaled." - hematology.org</span>
The exchange of matter or substances between the cell and its environment is dynamic as it varies in direction and rate as per the requirements of the cell. Thus,a cell attains a stead -state wherein the internal conditions of the cell remain constant. Hence, cell is considered to be a open dynamic system
Protoplanets are bodies or celestial objects which have the same size as the moon or a bit bigger. These bodies develop to eventually become planets. Therefore, the answer to this item is most likely letter D. outer planets.
