Which, if any, of the following situations represent improper segregation of functions?
a. The billing department prepares the customers’ invoices, and the accounts receivable department posts to the customers’ accounts.
b. The sales department approves sales credit memos as the result of product returns, and subsequent adjustments to the customer counts are pet-formed by the accounts receivable department.
c. The shipping department ships goods that have been retrieved from stock by warehouse personnel.
d. The general accounting department posts to the general ledger accounts after receiving journal vouchers that are prepared by the billing department.