Thanks for the question! So we’re being asked here for something that’s true of the typical adult canary during the late summer and fall. Take a look at lines 21024, where we’re told that “after the breeding season” happens during the late summer and fall. And then take a look at lines 35-38, which tells us that the number of neurons drops after the breeding season. So the regions that are necessary to learn songs decrease in size, which is what (D) says.
(A) is wrong because the fully structured and stable quality of the canary’s song repertoire comes in the winter and spring, not the late summer and fall. See the end of the second paragraph.
(B) is wrong because the neurons are generated during the winter and spring.
(C) is wrong because we’re never told that the songs are based on the models of other canaries.
(E) is wrong because the canaries learn an “entirely new repertoire,” see line 27.
Hope this helps! Feel free to ask any other questions that you might have.
