Final answer:
The least appropriate criterion against which to assess current controls in an internal audit engagement is industry best practices.
Step-by-step explanation:
The least appropriate criterion against which to assess current controls in determining 'what should be' during an internal audit engagement is a. Industry best practices. While industry best practices may provide valuable insights, they may not be directly applicable to a specific organization's unique circumstances and needs. Control policies and procedures prescribed by senior management, a standard of control effectiveness determined by the internal audit function, and the controls documented as being in place during the last audit are more tailored and relevant criteria.