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Answer:
The correct answer would be B. semi-permeable.
Plasma membrane of any cell including red blood cell is semi-permeable in nature as it is made up of lipid bilayer.
It permits the passage of certain substances across the membrane while it blocks other substances.
Gases, small uncharged or non-polar substances such as oxygen, carbon dioxide, et cetera can easily pass through the cell membrane of a cell.
Large or charged molecules such as proteins, sodium ions, potassium ions et cetera can not pass through the cell membrane. They require carrier proteins to pass through the membrane.
Plant cells have a cell wall, but animals cells do not. Cell walls provide support and give shape to plants. Plant cells have chloroplasts, but animal cells do not.
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The question is asking the determine the role that the United States do in the ecosystem base on the passage and situation in the question that you have state, base on my research, I would say that its role is a Dominant. I hope you are satisfied with my answer and feel free to ask for more if you have question and further clarification