The unified cell theory states that: all living things are composed of one or more cells; the cell is the basic unit of life; and new cellsarise from existing cells. Rudolf Virchow later made important contributions to this theory. ... Thecell is the fundamental unit of structure and function in living things.
The smallest and most exclusive grouping category is species.

Last option: Preserve an ecosystem

• The establishment of a bird reservation is a way to preserve an ecosystem because reservation provides suitable environment to organism. A healthy ecosystem means large number of biodiversity.
The answer would be (C.cat) because <span>For the cat has the most advanced biological system, whereas the unicellular algae and bacteria are microscopic in size, and while the ant does have a system and is a multi-cellular organism, the cat has a much more advanced biological system with many more functions and organs.
Hope it helps!
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