Which of the Following Is Not a Disadvantage of Firewalls

Which of the following is not a disadvantage of firewalls that act as packet filters?

A) Packet-filtering routers often are the first layer of network defense.
B) An administrator might miss some important rules,which would leave a hole in the firewall.
C) Because the content of a packet is irrelevant to a packet filter,once a packet is let through the firewall,the inside network is open to data-driven attacks.
D) An administrator might incorrectly specify a rule creating a vulnerability.