Classical Psychophysicists Placed a Great Deal of Emphasis on Determining

Classical psychophysicists placed a great deal of emphasis on determining the absolute threshold for a particular type of sensory stimulation. This proved to be difficult because

A) the point at which an observer detects a stimulus varies from trial to trial.
B) adequate technical equipment for measuring intensity was not available until recently.
C) subjects must be carefully trained to make these judgments accurately.
D) researchers used samples too small to give reliable results.