Answer: B. Acute hepatitis B.
Acute hepatitis A is characterized by IgM to hepatitis A. Prior infection is determined by IgG antibody.
Acute hepatitis B is characterized by the presence of surface antigen and IgM antibody to core antigen. Surface antigen alone may be absent late in the course of the disease or may present chronically unrelated to the current episode.
IgG to the core antigen indicates previous infection. IgG to the surface antigen is the best marker for immunity.