The question is not telling you what state the port is being reported by the scanning utility, if the program used to conduct this is nmap, nmap will show you one of three states - "open", "closed", or "filtered" a port can be in an "open" state yet filtered, usually by a stateful packet inspection filter (ie. Netfilter for linux, ipfilter for bsd). C and D to make any sense for this question, their bogus, and B, "You cannot spoof + TCP", well you can spoof + TCP, so we strike that out.

Linux passwords are enrcypted using MD5, DES, and the NEW addition Blowfish. The default on most linux systems is dependant on the distribution, RedHat uses MD5, while slackware uses DES. The blowfish option is there for those who wish to use it. The encryption algorithm in use can be determined by authconfig on RedHat-based systems, or by reviewing one of two locations, on PAM-based systems (Pluggable Authentication Module) it can be found in /etc/pam.d/, the system-auth file or authconfig files. In other systems it can be found in /etc/security/ directory.

Tripwire generates a database of the most common files and directories on your system. Once it is generated, you can then check the current state of your system against the original database and get a report of all the files that have been modified, deleted or added. This comes in handy if you allow other people access to your machine and even if you don't, if someone else does get access, you'll know if they tried to modify files such as /bin/login etc.

fragroute intercepts, modifies, and rewrites egress traffic destined for a specified host, implementing most of the attacks described in the Secure Networks "Insertion, Evasion, and Denial of Service: Eluding Network Intrusion Detection" paper of January 1998. It features a simple ruleset language to delay, duplicate, drop, fragment, overlap, print, reorder, segment, source-route, or otherwise monkey with all outbound packets destined for a target host, with minimal support for randomized or probabilistic behaviour. This tool was written in good faith to aid in the testing of network intrusion detection systems, firewalls, and basic TCP/IP stack behaviour.