Answer: The sentence that supports the idea that historic landmarks in Athens are in danger is B. The Parthenon, the temple to goddess Athena atop the Acropolis, is deteriorating due to pollution and acid rain.
Step-by-step explanation: The sentence that supports the central idea is B. as it is the only one that refers to an actual feature of a landscape that is in danger. The object to which option B. makes reference is the Parthenon, a historical temple located in Athens. Moreover, B. argues that the Parthenon is in danger due to "pollution and acid rain". In contrast, the other options do not refer to an object in danger: A. talks about Athens' population, while C. and D. make reference to important turning points in Athens' history.