In the order goods stage of the expenditure cycle, which of the following is designed to reduce the risk of collusion and fraud? 

Select one: 

a. Purchase orders are raised only once each week. 

b. Purchase order forms are pre-numbered. 

c. The person who places orders is different from the one who is responsible for maintenance of the list of approved suppliers. 

d. The decision to purchase more goods or materials is made by the purchasing officer.