Henry, a forensic investigator, is analysing a system suspected of being compromised by a stealthy...

Option A. Volatility is the best answer because CHFI v11 explicitly includes Windows Memory Analysis and Registry Analysis , Tools to Perform Windows Memory and Registry Analysis , Tools to Acquire Memory Dumps , and Tools to Examine the Memory Dumps . A stealthy rootkit that hides processes and files is exactly the type of threat that often requires deep memory-based analysis to uncover.

Volatility is built for memory forensics and can reveal hidden processes, injected code, loaded modules, suspicious drivers, and related artifacts that ordinary user-mode tools may not show. While Reg Ripper is excellent for registry artifact extraction, it is limited to registry-focused analysis and does not provide the full memory-inspection capability needed for a hidden rootkit case. DumpIt is mainly for acquiring memory, not analyzing it. Autopsy is useful for disk and file-system evidence but is not the strongest choice for rootkit-focused memory analysis.

Because Henry needs the best tool for memory and registry-oriented rootkit investigation , the strongest CHFI-aligned answer is Volatility .