Which is true about the web container request processing model？（）
A. The init method on a filter is called the first time a servlet mapped to that filter is invoked.
B. A filter defined for a servlet must always forward control to the next resource in the filter chain.
C. Filters associated with a named servlet are applied in the order they appear in the web application deployment descriptor file.
D. If the init method on a filter throws an UnavailableException， then the container will make no further attempt to execute it.
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