Which of the following is true about a firewall?

answer

Firewalls protect against email spoofing attacks.

Implicit deny is used to deny permissions to a specific user even when the rest of the user's group is allowed access.

Host$-$based firewalls and network$-$based firewalls can be installed separately, but they cannot be placed together to provide multiple layers of protection.

You must manually specify which traffic you want to allow through the firewall. Everything else is blocked.