In the 1990s, Deaths from Cocaine Overdosed Decreased Dramatically

In the 1990s, deaths from cocaine overdosed decreased dramatically. Clearly, fewer people were using cocaine in the 1990s than in previous decades.
The conclusion in the passage's argument is properly drawn if which of the following is assumed?

A) The number of cocaine overdose deaths reliably estimates the number of cocaine users.
B) Many cocaine users overdose more than once.
C) The potency of cocaine has remained relatively consistent for the past few decades.
D) Drug users overdose from cocaine at similar rates to that of other drugs.
E) Medical personnel can reliably test whether a death is due to an overdose or to other complications related to cocaine usage.