TOEFL Listening: TPO-TOEFL阅读TPO - 4F_1R0ZUAC4126AGN$

The experiment described in paragraph 2 supports which of the following conclusions? A. Predators are unable to distinguish between the begging cheeps of ground-nesting and those of tree-nesting warblers except by the differing frequencies of the calls. B. When they can find them, predators prefer the eggs of tree-nesting warblers to those of ground-nesting warblers. C. The higher frequencies of the begging cheeps of ground-nesting warblers are an adaptation to the threat that ground-nesting birds face from predators. D. The danger of begging depends more on the frequency of the begging cheep than on how loud it is.