Which statement is true of firewalls?

a$.$

They can identify attack signatures, trace patterns, and generate alarms for a network administrator.

b$.$

They cause routers to terminate connections with suspicious sources.

c$.$

They protect against external access, but they leave networks unprotected from internal intrusions.

d$.$

They monitor network traffic and use the $$prevent$,$ detect, and react$$ approach to security.