TOEFL Listening: TPO-TOEFL阅读TPO - FA135E44044X28Q7N$

In paragraphs 4 and 5, what evidence supports the claim that the intensity of nestling begging calls is a good indicator of which offspring in a nest would most benefit from a feeding? A. When placed in a nest with hungry robins, well-fed robins did not beg for food. B. Among robin nestlings, the intensity of begging decreased the more the nestlings were fed. C. Hungry tree swallow nestlings begged louder than well-fed nestlings in the same nest. D. Hungry tree swallow nestlings continued to beg loudly until they were fed whereas well-fed nestlings soon stopped begging.