D
Between 1971 and 1975, the government office that monitors drug companies issued an average of 60 citations a year for serious violations of drug-promotion laws. Between 1976 and 1980, the annual average for issuance of suchs citations was only 5. This decrease indicates that the government office was, on average, considerably more lax in enforcing drug-promotion laws between 1976 and 1980 than it was between 1971 and 1975. The argument assumes which one of the following?
A: The government office should not issue more than an average of 5 citations a year to drug companies for serious violations of drug-promotion laws.
B: Before 1971 the government office issued more than 60 citations a year to drug companies for serious violations of drug-promotion laws.
C: A change in enforcement of drug-promotion laws did not apply to minor violations.
D: The decrease in the number of citations was not caused by a decrease in drug companies' violations of drug-promotion laws.