The best answer is A. presence of nucleic acid.
Justification:
While all cellular microorganisms (such as bacteria, fungi, and protozoa) are made up of cells and can replicate independently, viruses are fundamentally different because they lack cellular structures and cannot reproduce independently. They require a host cell to replicate.
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B. ability to reproduce independently: Viruses cannot reproduce independently; they need to infect a host cell to replicate, which is a crucial distinction from cellular microorganisms that can reproduce on their own.
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C. sensitivity to antibiotics: Viruses are not affected by antibiotics, which typically target bacterial processes. While this is a distinction between viruses and bacteria, it does not highlight the fundamental difference between viruses and all cellular life forms.
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D. possession of a lipid membrane: Viruses can have lipid envelopes, but not all viruses do; furthermore, cellular microorganisms are also often associated with lipid membranes. This feature does not distinctly separate viruses from all cellular microorganisms.
Therefore, the presence of nucleic acid as the genetic material (either DNA or RNA) is the key characteristic that distinguishes viruses from all cellular microorganisms.