Question $8(3$ points$)$

Which scenario does NOT describe an external mechanism controlling the cell cycle?

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a Growth factors are added to a culture dish of normal cells, causing the cells to divide.

$$ b Normal cells get crowded by their neighbors and stop dividing.

c A normal cell is not the right eize and is stopped at the Gy checkpoint.

o All three scenarios include an axtemal mechanism fontroling the cell cycle.