OG9 阅读 Q51

Choice C is the best answer. According to the last sentence of the fifth paragraph of Passage 1, "Mice infected with bacteria that cause upper respiratory tract infections . . . were treated with teixobactin, and the drug knocked out the infections with no noticeable toxic effects." The second paragraph of Passage 2 explains that teixobactin was tested in a laboratory and killed gram-positive bacteria, but, according to the fourth sentence of the third paragraph, it "doesn't kill the Gram-negative opportunists as it is too big to cross their complex cell wall." Therefore, since teixobactin was not successful in eradicating gram-negative bacteria as stated in Passage 2, this information best supports the conclusion that the mice described in the experiment in Passage 1 had upper respiratory tract infections that were likely not caused by gram-negative bacteria since these infections were successfully treated by teixobactin.
Choices A, B, and D are incorrect because no information in Passage 2 supports the conclusion that the mice in the experiment described in Passage 1 were less susceptible to subsequent upper respiratory tract infections due to exposure to teixobactin (choice A), the gram-positive bacteria enhanced the effectiveness of teixobactin against the upper respiratory tract infections in the mice (choice B), or the teixobactin attacked the proteins of the bacteria that caused the upper respiratory tract infections in the mice.