In a research study, if we can not determine which variable is causing which, it is called the problem.

The herpes viruses are important enveloped dna viruses that cause disease in vertebrates and in some invertebrates such as oysters. some of the human forms are herpes simplex virus (hsv) types i and ii, causing facial and genital lesions, and the varicella zoster virus (vsv), causing chicken pox and shingles. each of these three actively infects nervous tissue. primary infections are fairly mild, but the virus is not then cleared from the host; rather, viral genomes are maintained in cells in a latent phase. the virus can later reactivate, replicate again, and infect others. in electron micrographs of hsv infection, it can be seen that the intact virus initially reacts with cell surface proteoglycans, then with specific receptors. this is later followed by viral capsids docking with nuclear pores. afterward, the capsids go from being full to being "empty." which of the following best fits these observations? a) viral capsids are needed for the cell to become infected; only the capsids enter the nucleus. b) the viral envelope is not required for infectivity, since the envelope does not enter the nucleus. c) only the genetic material of the virus is involved in the cell's infectivity, and is injected like the genome of a phage. d) the viral envelope mediates entry into the cell, the capsid mediates entry into the nuclear membrane, and the genome is all that enters the nucleus.