Which life functions is a virus capable of performing?

Which life functions is a virus capable of performing?

Viruses are unique biological entities that are often considered to be on the border between living and non-living. They are obligate intracellular parasites, meaning they cannot carry out life functions independently.

• A. Viruses do not "feed" in the traditional sense; they lack the metabolic machinery for nutrient uptake and processing.
• B. While viruses do invade cells and can enter the nucleus to replicate their genetic material, "protecting its DNA" is not a primary life function in the context of what a virus performs as an active process, but rather a structural aspect of its capsid.
• C. Viruses cannot grow or reproduce outside of a living host cell because they lack the necessary cellular machinery.
• D. Viruses can only replicate (reproduce) and assemble new viral particles (a form of "growing" their population) by hijacking the machinery of a living host cell.

The final answer is $\boxed{\text{D. Growing and reproducing only when inside a host cell.}}$