Final answer:
Viruses require host cells for reproduction because they need to utilize the host's cellular machinery, lacking enzymes and the ability to make proteins on their own.
Step-by-step explanation:
Viruses most rely on host cells for reproduction because they lack the enzymes necessary for metabolism and have no structures to make protein. This means that viruses are essentially parasitic and require a host cell's machinery to replicate themselves. With this in mind, the correct answer is B) Lack the enzymes necessary for metabolism and have no structures to make protein. Viruses cannot replicate or produce protein without invading a host cell and utilizing its ribosomes, enzymes, and other cellular components.