Final answer:
Internal auditors may rely on external auditors' work to enhance efficiency if it is reliable. They assess the external auditors' work to ensure it is dependable and can be trusted before using it to supplement their own auditing efforts.
Step-by-step explanation:
To improve their efficiency, internal auditors may rely upon the work of external auditors if it is reliable. Effective internal auditing can leverage the independent verification provided by external auditors to avoid duplication of effort and focus on areas that may require more detailed internal examination. In practice, internal auditors evaluate the scope and accuracy of external auditors' work to determine its reliability before deciding to rely upon it.