详解
Choice D is the best answer. The author explains that Ken Dial created an experiment to study the evolution of flight by observing how baby Chukars learn to fly. During the experiment, Dial noticed the unusual way Chukars use their "wings and legs cooperatively" to scale hay bales (lines 38-43"their... possibilities"), and he created "a series of ingenious experiments" (line 46"series...as") to study this observation. After his additional experiments, Dial determined that these baby birds angle "their wings differently from birds in flight" (lines 49-50"to... and").
Choices A, B, and C are incorrect because they do not accurately reflect the sequence of events in the passage.