Evidence That the Development of Cancer Is a Multistep Process

Evidence that the development of cancer is a multistep process includes the:

A) observation that certain tumor-suppressor genes and oncogenes are involved in a sequential manner in the development of colon cancer
B) fact that proto-oncogenes are widely conserved in evolution
C) usual occurrence of retinoblastoma at a young age
D) development of a cancer as a result of activation of a single oncogene by any of a variety of mechanisms
E) fact that there are many genetic and epigenetic mechanisms that lead to inactivation of the same tumor-suppressor gene