Scientist: In our study, chemical R did not cause cancer in laboratory rats. But we cannot conclude from this that chemical R is safe for humans. After all, many substances known to be carcinogenic to humans cause no cancer in rats; this is probably because some carcinogens cause cancer only via long-term exposure and rats are short lived. Which one of the following most precisely describes the role played in the scientist's argument by the statement that chemical R did not cause cancer in laboratory rats?
A: It is cited as being insufficient to support the conclusion that chemical R is safe for humans.
B: It is advanced to support the contention that test results obtained from laboratory rats cannot be extrapolated to humans.
C: It is used as evidence to support the hypothesis that chemical R causes cancer in humans via long-term exposure.
D: It illustrates the claim that rats are too short lived to be suitable as test subjects for the carcinogenic properties of substances to which humans are chronically exposed.
Choose A, B, C or D as your solution.
A