The use of a firewall is a requirement to protect a local area network (LAN) that has external connections without that you have no real protection from fraudsters.
The following answers are incorrect:
dial-up. This is incorrect because this offers little protection once the connection has been established.
passwords. This is incorrect because there are tools to crack passwords and once a user has been authenticated and connects to the external connections, passwords do not offer protection against incoming TCP packets.
fiber optics. This is incorrect because this offers no protection from the external connection.