Because viruses could not be visualized using conventional microscopes further progress required the development of techniques for isolating,propagating and analyzing viruses.All of the following are true except:

A)crystal structure of the tobacco mosaic virus showed that it was made up of RNA and protein
B)viruses were first observed with an electron microscope
C)viral DNA has a different structure from that discovered by Watson and Crick
D)Hershey and Chase demonstrated that the genetic material of some viruses is DNA