Explanation
Correct answer: A.
Choice A is the best answer. Both texts state that tropical mountain bird species have limited ranges or habitats, although they disagree on the reason for this. Text 1 claims that temperature is the main factor that determines where these birds can live, while Text 2 claims that competition with other species is the main factor. However, both texts agree that these birds are not able to survive in many kinds of areas.
Why the other choices are wrong
Choice B
Choice B is incorrect. Neither text mentions the tools or methods that scientists use to observe these birds, either now or in the past.
Choice C
Choice C is incorrect. Neither text mentions anything about how these birds build their nests.
Choice D
Choice D is incorrect. Neither text provides any information about the genetic similarity of these birds, so we have no evidence that either author would agree with this statement.