In One of the Case Studies in the Textbook, Marcus

In one of the case studies in the textbook, Marcus Lane, a geologist for an environmental management and engineering services firm, traveled all over North and South America as part of his job, resulting in numerous expense reimbursements. Unfortunately, Lane went too far and began to double book his air travel using his personal credit card. He booked two separate flights to the same location, but with a huge cost difference. He used the cheaper ticket for the actual flight and returned the more expensive ticket for credit. And, of course, he submitted the more expensive ticket for reimbursement. How was his scheme detected?

A) The internal auditor discovered it during a routine audit of expense reimbursements.
B) The department's administrative assistant took a message from the travel agency about a trip that she knew Lane didn't take.
C) Lane's manager received an anonymous tip.
D) The external auditors discovered it while sampling expenses during their annual audit.