The correct answer is that viruses can infect bacteria, fungi, and plants, which highlights the broad host range of viruses. This phenomenon is due to the diverse mechanisms by which viruses attach to and penetrate host cells, utilizing cell-specific receptors. Understanding viral infections across these life forms is crucial in fields like medicine, agriculture, and microbiology, as it emphasizes the role of viruses in various ecological interactions and their impacts on health and food security, topics that are significant in the UPSC Prelims syllabus.