An attacker sends a low rate of TCP SYN segments to hosts， hoping that at least one port replies. Which type of an attack does this scenario describe？（）

A.DoS
B.exploit
C.propagation
D.port scanning
E.reconnaissance

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.

A.RADIUS
B.TACACS+
C.LDAP
D.IIS