Which two statements about the use of SCREEN options are correct？（）

• A、SCREEN options are deployed at the ingress and egress sides of a packet flow.
• B、Although SCREEN options are very useful， their use can result in more session creation.
• C、SCREEN options offer protection against various attacks at the ingress zone of a packet flow.
• D、SCREEN options examine traffic prior to policy processing， thereby resulting in fewer resouces used formalicious packet processing.