Answer:
A) Capsid
Step-by-step explanation:
A virus is an organism incapable of replicating on its own, hence, they perform this process by infecting a living host. The process of replication in a living host is their infection cycle. The infection cycle generally involves attaching to the membrane of its specific host, entry into the host cell, incorporate its genetic material into its host genome and replication itself.
However, attachment proteins in a structure of the viral cell makes it able to attach to the membrane of its host by binding to receptors on host's membrane. Viruses are host-specific. This specificity is achieved when a virus finds corresponding viral receptors on the host cell. The structure in the virus that enables it binds to receptor sites on its host is called CAPSID. The capsid is a Protein that encompasses the genetic material of the virus.