Final answer:
Prenumbered documents are only useful for control when the sequence is accounted for periodically, ensuring all documents are used in order and discrepancies are tracked.
Step-by-step explanation:
Prenumbered documents will only be useful for control purposes if the sequence is accounted for periodically. It is important that a company's internal control system includes procedures to ensure that all documents are used in the sequence provided and that any missing documents are investigated. This helps prevent fraud or errors, as it becomes easier to track down any discrepancies.
Allowing employees to use documents out of numerical sequence (option C) could create confusion and complicate the tracking process, potentially compromising the control purpose of prenumbering. Similarly, a different numerical sequence for each company (option A) or using the same numerical sequence for each accounting period (option D) isn't necessarily relevant to the effectiveness of the control as long as the numerical sequence is properly managed within each period for an individual company.