The correct comparison between a virus and a unicellular organism from your options is:
Unicellular organisms have a cell membrane made from a lipid bilayer; viruses have a protein coat.
This accurately describes a fundamental structural difference between the two. Unicellular organisms, like bacteria and protozoa, have a cell membrane that regulates what enters and exits the cell, while viruses are composed of genetic material encased in a protein coat and do not have a cell membrane.