Question

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viruses are difficult to control with antiviral medications, because
o they are infectious agents.
o they are relatively primitive microbes.
o their evolutionary relationships are difficult to trace.
o they have a protein coat.
o heritable alterations to their genomes occur frequently.

Explanation:

Viruses are difficult to control with antiviral medications mainly due to their high - mutation rate. Heritable alterations to their genomes occur frequently, which allows them to quickly develop resistance to antiviral drugs.

Answer:

heritable alterations to their genomes occur frequently.