TOEFL Reading: ETS-TOEFL阅读机经 - 2NK89117CP843L0RL$

According to paragraph 4, why have species of flightless and ground-nesting birds become so numerous on Oceanic islands? A. They have no predators on the islands. B. They were some of the strongest species to arrive on the islands. C. They live closer to their food sources than other species do. D. They are affected less by climatic changes than other animals are.