Explanation
9. As mentioned above, the first paragraph mentions various costs associated with birdsong, but from that point onward, the focus of the passage is on evidence concerning the energy costs of singing, for nightingales in particular. Thus, the correct answer is
Choice C. Although the passage mentions other costs, it does not compare them with one another, so Choice A is incorrect. Because the passage does not question any hypotheses, discuss benefits, or advance an alternative model of birdsong, Choices B, D, and E are incorrect.
10. Choice B is correct.
Choice A is incorrect: the only reference to thermoregulation comes in line 24 and discusses nighttime activity, not daytime activity.
Choice B is correct: the second paragraph explains that birds store energy as fat deposits that can be estimated by measuring body mass, and that body mass at dusk was significantly higher in nightingales on nights when their song rate was higher.
Choice C is incorrect: while the passage does say that singing exposes birds to predators (line 3), it says nothing to suggest that they make special efforts to hide before singing, and in fact it says that nightingales spend extra time foraging (line 20).
11. Only two sentences in the relevant portion of the passage contain information that might be considered to be empirical results. The last sentence of the first paragraph contains information about increases in energy consumption but only the
last sentence of the second paragraph provides results in support of the only hypothesis in the passage, that nightingales should lose more body mass on nights when their song rate is high. Thus,
sentence (“Thomas found . . . high”) is the correct choice.
12. Choice B is correct.
Choice A is incorrect: you might infer that energy costs of singing are significant but no information is given to suggest that they are greater than other costs.
Choice B is correct: lines 4–5 say that discussions of the costs of singing have generally focused on energy costs.
Choice C is incorrect: the only mention of differences across species occurs in the discussion of the findings of Eberhardt and Chappell. These findings relate to energy costs alone and, if anything, suggest that energy costs vary considerably.
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