A Billboard Is Positioned Correctly Beside a Busy Highway

A billboard is positioned correctly beside a busy highway. However, the merchant that has purchased the billboard is complaining that no response is being generated by his advertising message. Upon closer inspection, the billboard company determines that the typeface used is too small to be effectively read by a motorist going 60+ mph on the highway. Which of the following sensory thresholds would be most appropriate to explain the failure of this advertisement to connect with motorists?

A) the absolute threshold
B) the intensity threshold
C) the relative threshold
D) the exposure threshold
E) the differential threshold