Question

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

Explanation:

Viruses are microscopic entities that contain nucleic - acid (DNA or RNA) as their genetic material. They are not cells, so they are not prokaryotes. A virus has a protein capsid that may or may not be surrounded by an envelope (not a shell surrounding a capsid). Viruses are not considered living organisms in the traditional sense as they cannot carry out metabolic processes on their own. Bacteriophages are a type of virus that attacks bacteria, but not all viruses attack bacteria.

Answer:

A. A microscopic thing with a nucleic acid code