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 intensity threshold
B. the differential threshold
C. the absolute threshold
D. the relative threshold