Let's analyze each part of the sentence to identify the error.
Based on this analysis, part (a), "Finishing his breakfast," contains an error as the phrasing does not appropriately indicate a completed action for the context described. The correct option should be acknowledged for revision in test settings.
Therefore, the part containing the error is "Finishing his breakfast".
Identify the part of the sentence that contains an error:
"Neither the manager nor the employees ___ willing to accept the new policy."