Which of the following combinations of duties can the same employee perform without violating the principle of segregation of duties?

a. Shipping inventory and billing customers

b. Issuing credit memos and maintaining accounts receivable

c. Taking customer orders and checking inventory availability

d. All three of the listed combinations can be performed by the same person without violating the principle of segregation of duties

e. None of the three listed combinations should be performed by the same person because all three combinations violate the principle of segregation of duties