Final answer:
C) Frequency coding is the mechanism by which the modality of a stimulus can be determined within the central nervous system. Hence, C) is correct.
Step-by-step explanation:
The modality of a stimulus can be determined within the central nervous system by frequency coding. In sensory systems, the intensity of a stimulus is often encoded by the rate of action potentials produced by the sensory receptor.
A more intense stimulus will produce a higher rate of action potentials, while a less intense stimulus will produce a lower rate. This coding mechanism allows the central nervous system to distinguish between different stimuli based on their frequency of action potentials.