Explanation/Reference:
B: The default configuration of the XTM device is to block DDoS attacks.
C: In a flood attack, attackers send a very high volume of traffic to a system so it cannot examine and allow permitted network traffic. For example, an ICMP flood attack occurs when a system receives too many ICMP ping commands and must use all of its resources to send reply commands. The XTM device can protect against these types of flood attacks: IPSec, IKE, ICMP. SYN, and UDP.
E: When the Block Port Space Probes (port scans) and Block Address Space Probes check boxes are selected, all incoming traffic on all interfaces is examined by the XTM device.
CG: Default packet handling can reject a packet that could be a security risk, including packets that could be part of a spoofing attack or SYN flood attack
Reference: http://www.watchguard.com/help/docs/wsm/xtm_11/en-US/index.html#en-US/ intrusionprevention/default_pkt_handling_opt_about_c.html%3FTocPath%3DDefault%2520Threat%
2520Protection%7CAbout%2520Default%2520Packet%2520Handling%2520Options%7C_____0