GRE Reading Comprehension: OG/PP2-GRE阅读OG/PP2 - 2JAH2IZ0J6PN227NP

The primary purpose of the passage is to A. compare the different types of cost involved for certain birds in singing B. question a hypothesis regarding the energy costs of singing for certain birds C. present evidence suggesting that singing has an important energy cost for certain birds D. discuss the benefits provided to an organism by a behavior that is costly in energy E. describe an experiment that supports an alternative model of how birdsong functions