Which of the Following Statements Is True of Firewalls

Which of the following statements is true of firewalls?

A) They protect against external access, but they leave networks unprotected from internal intrusions.
B) They can identify attack signatures, trace patterns, and generate alarms for a network administrator.
C) They monitor network traffic and use the "prevent, detect, and react" approach to security.
D) They cause routers to terminate connections with suspicious sources.