What is the main reason that viruses are not considered to be living
organisms?
A They are too small to be living.
B They do not have DNA.
C They need the host cell to replicate.
D
They kill the host cells.

C. They need a host cell to replicate.

Explanation:

In order for an organism to be considered living it must be able to reproduce on with its own species or on its own, (sexually and asexually) which is why we consider viruses not to be living.

a tetrad is the foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.