Final answer:
The main difference is that viruses can exit the host cell and infect other cells, whereas mobile genetic elements cannot. Viruses rely on the host's cellular machinery for reproduction, while mobile genetic elements typically alter the host genome from within a single cell.
Step-by-step explanation:
The defining difference between viruses and mobile genetic elements is that viruses can leave the cell and move to other cells and organisms, while mobile genetic elements generally move around the genome within a cell. This is reflected in choice C of the provided options. Viruses are considered obligate intracellular parasites that must infiltrate living cells to replicate their proteins and copy their genomes. They use the host cell's machinery, like ribosomes and enzymes, to produce more viral particles. In contrast, mobile genetic elements are DNA sequences that can change their position within the genome of a single cell, thereby potentially altering the genome of that host cell.
Moreover, viruses exhibit a variety of genome types, including DNA or RNA, which can be single-stranded or double-stranded. Viruses rely heavily on the host cell's machinery for replication, transcription, and translation, whereas mobile genetic elements use the host's replication machinery but do not typically form particles that can infect other cells.