Ooof what a question. after chatting with many AIs and digging into my A+,Net+,Sec+,Cysa+ studies I think this explanation makes me pick D
SYNFIN Scan (Option D):
Stealthiest approach: Sends only a SYN and FIN packet, which is often ignored by firewalls and IDSes.
Doesn't complete a full TCP handshake: Reduces the likelihood of detection.
Effective for mapping ports and firewalls: Reveals open and closed ports without raising alarms.
Other Options and Their Limitations:
Fast Scan (Option A): Quick but less stealthy, as it sends more probes that can be noticed. (there was another question where the answer was actually -f for stealth i think -f is still stealthy but just not as good as SYNFIN)
Data Length Adjustment (Option B): Can evade some detection techniques, but not as robust as SYNFIN.
Decoy Scan (Option C): Uses decoy IP addresses to obscure the source, but can still be detected if analyzed carefully.
In summary, the SYNFIN scan is the most effective choice for avoiding detection due to its unique approach and incomplete handshake behavior.