Final answer:
The percentage of high school seniors attitudinally disapproving of illicit drug use decreased between the mid-1970s and the late 1970s.
Step-by-step explanation:
The percentage of high school seniors attitudinally disapproving of illicit drug use between the mid-1970s and the late 1970s decreased.
During this time period, there was a significant increase in drug use, particularly with substances like marijuana and cocaine. This led to a more permissive attitude towards illicit drug use, especially among young people. The cultural and social changes of the era contributed to a decrease in disapproval of drug use among high school seniors.