For many cities in the world, there is no room to spread out further, _______ New York is an example

For many cities in the world, there is no room to spread out further, _______ New York is an example.
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A.for which

B.in which

C.of which

D.from which

答案及解析： C

解析：考查非限制性定语从句，从句还原后成为 “New York is an example of many cities”，所以选择介词of。