blcok extra urls in NGINX Reverse proxy

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http://serverfault.com – I use the nginx server in doing the Reverse proxy to http://abc.xxxx.com, but the urls includes the google ads urls http://pagead2.googlesyndication.com/pagead/show_ads.js, i want to block its ads. i try server methods,however,it cant do that. Giving me your support,thanks. (HowTos)