Rats injected with morphine exhibit decreased activity of the immune system, the bodily system that fights off infections. These same rats exhibited heightened blood levels of corticosteroids, chemicals secreted by the adrenal glands. Since corticosteroids can interfere with immune-system activity, scientists hypothesized that the way morphine reduces immune responses in rats is by stimulating the adrenal glands to secrete additional corticosteroids into the bloodstream.
Which of the following experiments would yield the most useful results for evaluating the scientists' hypothesis?
-
AInjecting morphine into rats that already have heightened blood levels of corticosteroids and then observing their new blood levels of corticosteroids
分析该选项
-
BTesting the level of immune-system activity of rats, removing their adrenal glands, and then testing the rats' immune-system activity levels again
分析该选项
-
CInjecting rats with corticosteroids and then observing how many of the rats contracted infections
分析该选项
-
DRemoving the adrenal glands of rats, injecting the rats with morphine, and then testing the level of the rats' immune-system responses
分析该选项
-
EInjecting rats with a drug that stimulates immunesystem activity and then observing the level of corticosteroids in their bloodstreams
分析该选项