The correct answer is D because PowerShell script block logs provide the most direct visibility into PowerShell-based attacker activity. In CEH-style security operations and incident response, defenders must review logs that are closest to the suspicious activity being investigated. PowerShell is widely used for Windows automation, administration, and post-compromise actions; the CEH-related material notes that PowerShell can automate tasks on Microsoft Windows systems and can be used after compromising a Windows target. Script block logging records the actual PowerShell code blocks executed, including suspicious commands, encoded commands, download cradles, privilege escalation scripts, and in-memory execution attempts. DNS logs may show domain lookups, and firewall logs may show network connections, but neither reveals the PowerShell commands themselves. Syslog is generic and more common in Unix/Linux or centralized logging contexts. Since the attacker is abusing PowerShell heavily, PowerShell script block logs give investigators the strongest evidence of command content, execution behavior, and malicious intent.
Therefore, option D is the best answer.