According to the passage, which one of the following is true of the typical adult canary during the late summer and fall? A. The canary's song repertoire takes on a fully structured and stable quality. B. A process of neurogenesis replaces the song-learning neurons that were lost during the preceding months. C. The canary begins to learn an entirely new repertoire of songs based on the models of other canaries. D. The regions in the canary's brain that are central to the learning of song decrease in size. E. The canary performs slightly modified versions of the songs it learned during the preceding breeding season.