Why Do V-Oncs Cause Cancer Whereas Normal C-Oncs Do Not

Why do v-oncs cause cancer whereas normal c-oncs do not?

A) More than one v-onc occurs in the tumor cell.
B) C-oncs are never expressed except when infected by a retrovirus.
C) Expression of both the v-onc and the c-onc is enough to cause transformation.
D) The v-oncs are expressed at much higher levels from the strong retroviral promoter than are c-oncs.
E) All of these are correct.