Final answer:
The changes in a plant host due to a viral infection facilitate the virus's transmission and replication, not the host's reproductive capabilities, resistance to pathogens, or lifespan.
Step-by-step explanation:
In the example of host manipulation involving a plant and a virus, the changes benefited the virus because C) They facilitated the virus's transmission and replication. Viruses evolve to enhance their own survival and replication capabilities, often at the expense of their host's health. Although these changes may not directly enhance the host's reproductive capabilities or its resistance to other pathogens, they can significantly improve the virus's ability to spread.
This is also not primarily about increasing the host's lifespan, but about maximizing viral proliferation. Plant viruses, such as the tobacco mosaic virus with its single-stranded RNA genome, often alter the structure and function of their host to optimize their transmission by vectors such as insects or through direct contact with damaged plant tissues. An important example of this is in the way that some plant viruses can modify the plasmodesmata to facilitate cell-to-cell movement within the plant.