Final answer:
Segregation of duties is violated as the clerk is tasked with both custody of cash receipts and recording, which are incompatible duties in the revenue process, leading to potential for fraud or errors.
Step-by-step explanation:
The violation of segregation of duties occurs in the scenario provided because the same clerk is responsible for both issuing customer invoices and statements, and collecting cash receipts. These responsibilities should be separated to prevent possible fraud or errors. The correct answer is that the clerk holds the incompatible duties of custody and recording. In sound internal controls practices, the individual who has custody of assets (in this case, cash receipts) should be different from the one who is responsible for the recording or documentation part (issuing invoices and statements) of the revenue process.