The correct answer is A. The passage describes how the absence of human actitvity will change Central Park to show that nature will eventually destroy what people have built.The notion of absence of human activity is present in the fact that the author points out that the parks´s ponds and reservoirs are not being dredged so have reincarnated into marshes.
The idea that nature will eventually destroy what people have built is conveyed when a maturing forest that invades streets and foundations is described.