Which of these is one of the main reasons why viruses are not classified as living organisms?
A) viruses can evolve
B) viruses are single-celled
C) viruses contain DNA or RNA
D) viruses are not made of cells

D

Explanation:

A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Although they have genes, they do not have a cellular structure, which is often seen as the basic unit of life. Viruses do not have their own metabolism, and require a host cell to make new products. They therefore cannot naturally reproduce outside a host cell.

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