Final answer:
For initial access during a security assessment without credentials, the audit team could use Social Engineering and Reconnaissance, as these methods gather information and exploit human factors to gain unauthorized access.
Step-by-step explanation:
The question relates to network security assessments where an audit team aims to gain initial access to a system to test its vulnerabilities. Without having access credentials, the methods they could use from the options provided are B. Social engineering and D. Reconnaissance.
Social engineering involves manipulating individuals into providing confidential information. This may involve tricking someone into giving away passwords or creating a scenario where credentials are divulged. On the other hand, reconnaissance is about gathering as much information as possible about the target network, which might include identifying open ports, services running, and vulnerabilities that can be exploited for access.
Methods like Tabletop exercises are more about planning and strategy rather than active penetration methods, and Runtime debugging, Code review, and using a Remote access tool would typically require some level of pre-existing access or detailed knowledge of the system's internal workings.