Which of the following statements correctly describes the regulation of cell division?

Which of the following statements correctly describes the regulation of cell division?

   A. Cells will divide continuously until they encounter an inhibitory signal.
    B. Cells divide when division is favored by the sum of multiple signals.
    C. Transcription of growth-promoting genes is enhanced by growth factors and inhibited by growth- inhibiting factors.
    D. A given cell displays receptors for and responds to either growth factors or growth-inhibiting factors.

The binding of extracellular growth factors to cell surface receptors ultimately results in the expression of a specific gene or genes. This fact suggests all of the following except that _______.

   A. factors influencing a cell's "decision" to divide are initiated outside the cell
    B. these receptors span the cell membrane
    C. the initial signal is relayed to the cell nucleus
    D. the signal cannot be turned off