Final answer:
Mitogens are a class of signal molecules that stimulate cell division by releasing the molecular brakes that keep cells in the G0 or G1 phase of the cell cycle.
Step-by-step explanation:
The correct answer is mitogens. Mitogens are a class of signal molecules that stimulate cell division by releasing the molecular brakes that keep cells in the G0 or G1 phase of the cell cycle. They promote cell growth by activating cell-surface receptors and initiating signaling pathways that result in the expression of proteins involved in cell division.