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.