Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected white-footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease would likely decline. Which of the following, if true, most strengthens the argument? A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes Lyme disease in humans. B. There are no known cases of a human’s contracting Lyme disease through contact with white-footed mice. C. A deer tick feeds only once while in the larval stage. D. A single host animal can be the source of bacterium for many tick larvae. E. None of the other species on which deer tick larvae feed harbor other bacteria that ticks transmit to humans
Mice that have been given morphine are very likely to develop blood poisoning because bacteria that normally reside in the intestine typically respond to morphine by migrating into the bloodstream. However, when mice are given both morphine and the new drug naltrexone, blood poisoning is much less frequent, although it does still occur. These results provide support for researchers' prediction that naltrexone will turn out to be toxic to certain types of bacteria.
Which of the following, if discovered to be true, would most seriously weaken the support for the researchers' prediction?
A: After being administered to mice, naltrexone does not pass from the bloodstream into the intestine. B: Naltrexone inhibits morphine from triggering the migration of intestinal bacteria into the bloodstream. C: Mice that have been given naltrexone but not morphine have no greater risk of developing blood poisoning than do mice that have not been given either substance. D: The increased risk of blood poisoning is not the only harmful effect on mice of being given morphine. E: Conditions other than the presence of intestinal bacteria in the bloodstream can cause blood poisoning in mice.
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发表于 2011-7-22 09:17:38
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