What is a Firewall? (you may choose multiple answer)

a. A firewall is mostly used to protect the system or network from malware, worms, and viruses. Firewalls can also prevent content filtering and remote access. b. A firewall is a tool that shows the packet path. It lists all the points that the packet passes through. c. A firewall is used mostly when the packet does not reach the destination. d. A firewall is used to check where the connection breaks or stops or to identify the failure. e. A firewall is set on the boundaries of any system or network which monitors and controls network traffic.