A zero-day vulnerability is discovered that affects a specific network device. This vulnerability only affects services on port 21. This network device is restricted to use only secure protocols and services. Which of the following explains why this device is secure? 

Answer options:

A. Because secure protocols would reject malicious packets
B. Because SCP is not a secure service
C. Because FTP is not a secure service
D. Because a secure firewall will protect the device

C