The best answer to fill in the blank is "multilayered membrane."
I’m not exactly sure, but I’m thinking it may be A . I just learned about this unit previously .
Answer: C
Explanation: Smaller single-celled organisms have a high surface area to volume ratio, which allows them to rely on oxygen and material diffusing into the cell (and wastes diffusing out) in order to survive. The higher the surface area to volume ratio they have, the more effective this process can be.
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