What is directly responsible for an acquired trait

You've failed to list answer choices, but it is environment, as an acquired trait, that mean you've got it on your own, not by genes meaning it's not inherited. The others are all inherited traits, which come from the parents.

When a virus infects a host cell, it uses the cell's machinery to make copies of its own genetic material in a process called replication. finally, during the process of self-assembly, that protein shell and the copies of the virus's genetic material are assembled into new viruses.