Final answer:
Mark should report the suspected payslip fraud to the appropriate authorities.
Step-by-step explanation:
When Mark noticed something odd with Vivien's payslips, he believed they were fraudulent. In this situation, Mark should report his suspicions to the appropriate authorities, such as the police or his local banking regulatory agency. It is important for Mark to act ethically and ensure that the loan application process remains fair and transparent. By reporting the potential fraud, Mark is taking the necessary step to protect the interests of the bank and maintain the integrity of the loan approval process.