In the Context of the Difference Threshold, Identify the Correct

In the context of the difference threshold, identify the correct statement. 

A) Weber's constant is especially accurate when comparing extremely bright or extremely dull lights. 
B) On average, people can tell when a tone rises or falls in pitch by an extremely small one-third of 1 percent. 
C) On average, people can detect differences in saltiness of less than 10 percent. 
D) Ernst Weber discovered through laboratory research that the threshold for perceiving differences in the intensity of light is about 20 percent of their intensity.