Cancerous cells, and how they divide

Today's question involves how cancerous cells divide and actually become tumors. Here's the question:

All of the following mechanisms have been shown experimentally to the contribution to the formation of cancer cells EXCEPT:
and then there were answers.

The basis of this question is the nature of cancer. Cancer is the abnormal growth (and possible spread) of cells. These cells can invade and destroy other, healthy tissues, which causes the pain and death of cancer. The question, then, is what actually causes cancer to develop?

Since its discovery, scientists have been studying the mechanism of cancer. Their experiments have been focused on both the destruction of cancerous cells, and the mechanisms needed to cause normal cells to turn cancerous. There are several ways your normal tissues can cause you problems:

1) DNA becomes damaged. All cells (with the exception of mature red blood cells) have a nucleus, and this nucleus contains the blueprint for the cells. If the portion of the blueprint that tells the cells when to stop producing gets damaged, then the cells keep dividing with no limit. That causes tumors.

2) Growth factors. Growth factors are natural proteins that stimulate reproduction and differentiation. The presence or absence of growth factors accounts for how often the cell reproduces.

3) Introduced DNA. Viruses have the annoying tendency to inject their DNA into other cells. While some viruses compeletly take over the cellular functions, some just incorporate themselves into the host DNA and for long periods of time. This foreign DNA can cause cells to react strangly, and can cause cancerous cells to develop. (Heard of the shot developed to prevent cervical cancer? That works on this basis).

These are three major factors that determine if a cell is going to turn cancerous. Now, back to our question:

All of the following mechanisms have been shown experimentally to the contribution to the formation of cancer cells EXCEPT:

A) Abnormally high energy reserves in cancer cells that cause them to divide too quickly
B) Mutations that cause excess production of growth factors by cancerous cells
C) Mutations that inactivate genes that normally inhibit cell reproduction
D) Mutations that reduce the need for growth factors in cells
E) Viruses that carry genes that transform normal cells into cancer cells

Which one of these wasn't mentioned above? A. There we go!