Answer:
The correct answer is option a) "Growth factor ligands do not bind as efficiently to receptors".
Explanation:
Growth factors are proteins that have a key role on cell's growth, survival and differentiation. Growth factors' activity is achieved by cell signaling processes, by interacting with receptors that transmit information to the intracellular space. Therefore, if it is found on aged cells that growth factor ligands do not bind as efficiently to receptors, it will be evidence that cell's signaling has been compromised.