TPO11 reading3问题求助

cjhjames89UID: 3000483

Given that predators can make it costly to beg for food, what benefit do begging nestlings derive from their communications? One possibility is that a noisy baby bird provides accurate signals of its real hunger and good health, making it worthwhile for the listening parent to give it food in a nest where several other offspring are usually available to be fed. If this hypothesis is true, then it follows that nestlings should adjust the intensity of their signals in relation to the signals produced by their nestmates, who are competing for parental attention. When experimentally deprived baby robins are placed in a nest with normally fed siblings, the hungry nestlings beg more loudly than usual—but so do their better-fed siblings, though not as loudly as the hungrier birds.

If parent birds use begging intensity to direct food to healthy offspring capable of vigorous begging, then parents should make food delivery decisions on the basis of their offsprings calls. Indeed, if you take baby tree swallows out of a nest for an hour feeding half the set and starving the other half, when the birds are replaced in the nest, the starved youngsters beg more loudly than the fed birds, and the parent birds feed the active beggars more than those who beg less vigorously.



It can be inferred from paragraphs 4 and 5 that parent songbirds normally do not feed
A. nestling that are too weak to beg for food as vigorously as their nestmates
B. more than one hungry nestling huring a single visit to the nest
C. offspring that were fed by the parents on the previous visit to the nest
D. nestling that have been removed and then later put back into their nest

纠结于A是从哪infer出来的...求指导~

dkflameUID: 2680233

the starved youngsters beg more loudly than the fed birds, and the parent birds feed the active beggars more than those who beg less vigorously.  
这里推得。。。