Answer: D) Not distinguishable by the sense.
Step-by-step explanation: the denotation of a word is its literal meaning, the definition that we can find in a dictionary, a word can have several denotations (or definitions). It is the contrary of connotation, which is the meaning given by the context or even by the readers (or listeners) based on their emotions or personal experiences. From the given options, the one that represents the definition (or denotation) of the word "imperceptible" is the corresponding to option D: Not distinguishable by the sense.