Option C. Sysmon is the best answer because CHFI v11 explicitly includes system behavior analysis involving monitoring files and folders , along with monitoring processes, services, startup programs, Windows event logs, API calls, and device drivers . In this scenario, Bob needs a tool that can log file and folder changes on a Windows system so he can understand how the malware modified the environment to hide itself.
Sysmon is designed to generate detailed system activity logs that can help investigators track suspicious changes and correlate them with process execution and other indicators of compromise. That makes it much more appropriate than the other choices. IDA Pro is primarily for reverse engineering binaries, EnCase is a broad forensic suite rather than a dedicated real-time system activity monitor, and FTK Imager focuses on imaging and evidence preview rather than ongoing change logging.
Because the question is specifically about monitoring and logging changes to files and folders , Sysmon is the most direct and CHFI-aligned answer for observing malware behavior at the system level.