Which of the following is typically a feature of viral infections?

Viral infections are characterized by the need for the virus to replicate within host cells. Viruses are obligate intracellular parasites, meaning they cannot reproduce independently outside of a host cell. Once inside a host, a virus hijacks the host's cellular machinery to replicate its nucleic acids and produce viral proteins, ultimately leading to the assembly of new virus particles. This process often causes harm to the host cells, contributing to the symptoms of the infection.

The other options don't align with the fundamental characteristics of viral infections. For instance, the production of spores is typically associated with certain bacteria and fungi, not viruses. Viruses also do not respond to antibiotics, which are specifically designed to target bacterial functions or structures. Lastly, while biofilms are communal structures formed by bacteria, especially in a host environment, viruses do not form biofilms as they lack the cellular structures necessary for such formations. Therefore, replication within host cells is the defining feature of viral infections.