Option A, opening the document on an air-gapped network, might mitigate the risk of spreading malware to other systems, but it still carries the risk of triggering malicious code within the document.
Option C, searching for matching file hashes on malware websites, could be useful for identifying known malicious documents but may not be effective against new or customized threats.
Option D, detonating the document in an analysis sandbox, involves executing the document in a controlled environment to observe its behavior. While this can provide valuable insights, it also carries the risk of inadvertently activating malicious code and spreading malware.
Therefore, option B is the best choice as it allows the security analyst to gather information about the document's potential malicious nature without executing any code.