Option A is the best answer because CHFI v11 explicitly includes "Perform Static and Dynamic Malware Analysis in a Sandboxed Environment," "Malware Analysis: Static and Dynamic," and the
"Prominence of Setting up a Controlled Malware Analysis Lab." These objectives show that the purpose of a sandbox is to let investigators safely run malware and observe what it does without putting production systems at risk.
A ransomware sample that evades traditional antivirus must be studied through controlled execution so analysts can identify file-encryption behavior, persistence mechanisms, dropped files, registry changes, process activity, and network communications. That is exactly what a malware sandbox is built for. It provides containment while allowing the forensic team to gather behavioral indicators and build defensive countermeasures.
Option B is unsafe and contrary to forensic practice. Option C misunderstands the purpose of sandboxing, and D refers to remediation rather than analysis. Therefore, under CHFI's malware-forensics objectives, the primary objective of using a malware sandbox is to execute and observe the ransomware in a controlled environment so its behavior can be understood and documented.