An audit team was testing source documents in the purchasing cycle and identified the following circumstances. Which of the following would be the most indicative of source document fraud? 

a. The same purchase order number appears on two invoices from the same vendor. 

b. The same item code appears on different invoices from the same vendor. 

c. The same invoice number appears on different invoices from the same vendor. 

d. The same invoice date appears on different invoices from the same vendor.