Which best describes a virus? a. a unicellular prokaryote b. a living organism that attacks bacteria c. a shell that surrounds a capsid d. a microscopic thing with a nucleic acid code

The correct answer is D. A microscopic thing with a nucleic acid code

Explanation:

Virus is a microscopic thing which has a nucleic acid surrounded by a proteinaceous coat called capsid. Viruses are parasites and are metabolically inactive outside their host therefore they are considered nonliving outside their host.  

When they come in contact with their host they inject their nucleic acid which can be DNA or RNA in their host. This viral genetic material incorporates in the host genome and replicated with host DNA. The virus that infects bacteria is called bacteriophage. So the correct answer is D.

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