How is this possible?

Refer to the to the network topology below.

You have IPS software Blades active on security Gateways sglondon, sgla, and sgny, but still experience attacks on the Web server in the New York DMZ.

How is this possible?
A . All of these options are possible.
B . Attacker may have used a touch of evasion techniques like using escape sequences instead of clear text commands. It is also possible that there are entry points not shown in the network layout, like rouge access points.
C . Since other Gateways do not have IPS activated, attacks may originate from their networks without any noticing
D . An IPS may combine different technologies, but is dependent on regular signature updates and well-turned automatically algorithms. Even if this is accomplished, no technology can offer 100% protection.

Answer: A