Viruses are known as obligate intracellular parasites because they cannot independently reproduce outside of a host cell.  Viral genomes (RNA or DNA) are enclosed by a protein shell called the capsid.  Some viruses, known as enveloped viruses, have an additional phospholipid bilayer that fully envelops the capsid.  Viruses that lack this outermost phospholipid covering are labeled non-enveloped.  The entry of either enveloped or non-enveloped viruses into a host cell enables the production of viral proteins and the subsequent assembly of viral progeny.Immune cells (eg, B cells, T cells) protect host organisms against viral infections by recognizing viral particles as foreign.  In response to the recognition of foreign particles, antigen-presenting cells ingest these particles and display cleaved antigen fragments on their surface for presentation to other immune cells.  The recognition of these displayed antigen fragments then enables the activation of other immune cells to stimulate an immune response, including the production of neutralizing antibodies.An example of an infectious viral disease is viral hepatitis (ie, inflammation of the liver), which can be caused by any one of five distinct hepatitis viruses (A through E) that infect hepatocytes (liver cells).  Hepatitis A, C, and E viruses (ie, HAV, HCV, and HEV, respectively) contain positive-sense, single-stranded RNA (+ssRNA) as genetic material.  In contrast, HBV has a partially double-stranded circular DNA genome.  HDV is unique because it has a negative-sense, single-stranded RNA (−ssRNA) genome.  None of these five viruses are retroviruses.Researchers hypothesized that synthetic antibodies could be used to treat viral hepatitis in patients with compromised immune systems.  Fluorescent antibodies were designed to bind the capsid proteins of the five hepatitis viruses and were tested by adding them to separate wells containing each type of virus.  The resulting fluorescence assay only detected bound antibodies in media with HAV or HEV.Adapted from Shin, E.C., Sung, P.S., & Park, S.H. (2016). Immune responses and immunopathology in acute and chronic viral hepatitis. Nature reviews. Immunology, 16(8), 509–523. Question 39Based on the passage, which of the following viruses does NOT have an outer phospholipid bilayer?A.HAVB.HBVC.HCVD.HDV