ALL PROTISTS ARE UNICELLULAR AND MICROSCOPIC IN NATURE, is the correct answer.
Protists are diverse collection of organisms which are primarily microscopic and unicellular in nature. Protists are scientifically categorized as eukaryotes and one definition of protists states that prosists are all eukaryotes organisms that are not animal, plant or fungi.
Respiratory system, because the lungs and diaphragm would get the oxygen from the air, and transfer them to the circulatory system (that's a pretty basic explanation, there's much more to it)
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