You Have a Permanent Connection to the Internet

Multiple Choice

You have a permanent connection to the internet. Your local network includes a web server and an SMTP server. You are concerned about hacking, so you set up port filtering on your network. Your local SMTP server has stopped sending or receiving messages through the internet, but your users can still access local and internet sites. What could be the possible cause?

A) Your DHCP server is down.
B) Your web server is filtering mail requests.
C) Your router is blocking port 25.
D) Your router is blocking port 110.