Read the following case study

Rachel Smith worked as an accounting manager for a large logistics company. She was considered a great employee; she worked hard and had not taken a vacation in 5 years. One of her responsibilities was to set up new suppliers in the accounts payable system. She also had the responsibility of approving invoices.

During this time, Rachel created several fake companies in their accounts payable system and approved several fake invoices. Rachel cashed the cheques issues for the fake invoices and stole the money.

a) Identify one internal control the business could have used to prevent the theft and explain why it would have prevented the theft.