In viruses, a combined structure formed by the core (nucleic acid) and the capsid is:

Explanation

Option A is correct. A nucleocapsid is the complex of viral nucleic acid (genome) and protein coat (capsid) that protects the genome and directs replication. Option B, the viral envelope, is a lipid bilayer derived from the host cell membrane and not the nucleocapsid. Option C, a capsomere, is just a protein subunit of the capsid, not the entire nucleocapsid. Option D, prions, are infectious proteins without nucleic acids and thus unrelated to nucleocapsids.