Answer:
The correct answer is a. Limits.
Step-by-step explanation:
The method of limits is one of the type's of testing that is commonly used in psychophysical investigation and research and helps to stablish the individuals level of stimulus perception.
In other words, a particular stimulus is manipulated by the researcher either by increasing it or decreasing it to stablish at which point the stimulus is perceptible or imperceptible to the subject.
In conclusion, the method of limits requires the experimenter to vary a perceptible stimulus until it is no longer perceived, or an imperceptible stimulus until it is finally perceived.