Answer:
Letter C
Step-by-step explanation:
Action potentials are certainly a key to understand neuronal signaling, and to this day, neuroscientists are still developing specific models to try decipher how much information a bunch of neuronal spikes has to inform in distinct neurons.
Interestingly, throughout evolution action potentials have proven to be a very efficient mechanism of communication, and their most studied and most important attribute has been proved to be frequency, which is a property that depends on the source only, ie it does not change until you reach your destination. So, the right answer is Letter C.