OG4 阅读 Q13

Choice A is the best answer. The author states that democratic inversion "can occur in cities that are growing, those whose numbers are flat, and even in those undergoing a modest decline in size" (lines 33-35,"it can ... size"). In this context, cities whose "numbers," or population size, are "flat" have static, or unchanging, populations.
Choices B, C, and D are incorrect because in this context, "flat" does not mean deflated, featureless, or obscure.