Which of the Following Best Describes a Firewall

Which of the following best describes a firewall?

A) Passive device that analyzes network traffic to detect unauthorized access
B) Active device that sits inline with traffic and can respond to intrusions by disabling the connection, dropping the packet, or deleting the malicious content
C) A software or hardware device that can filter incoming or outgoing traffic based on specific rules
D) A device that monitors the characteristics of a single host and the events occurring on that host