单选题 The number of hospital emergency room visits by heroin users grew by more than 25 percent during the 1980s. Clearly, then, the use of heroin rose in that decade.
The author's conclusion is properly drawn if which one of the following is assumed?

A、 Those who seek medical care because of heroin use usually do so in the later stages of addiction.
B、 Many heroin users visit hospital emergency rooms repeatedly.
C、 The number of visits to hospital emergency rooms by heroin users is proportional to the incidence of heroin usage.
D、 The methods of using heroin have changed since 1980, and the new methods are less hazardous.
E、 (E) Users of heroin identify themselves as such when they come to hospital emergency rooms.

【正确答案】 C

【答案解析】[解析] 本题应该注意的是：不是每一个服用了海洛因的人都到急诊室去就诊，因此要从急诊室这10年里海洛因服用者就诊的次数的增加，推出服用海洛因的整体人数都在增加，就必须指出到急诊室就诊的海洛因服用者与服用海洛因的总的人数之间的特定关系。在5个选项中只有(C)指出了这种特定关系，因此，正确选项为(C)；其余四个选项都不是本题结论所依赖的假设。