Final answer:
The key segregation of duties for the revenue process is to ensure that different parties are responsible for different tasks to minimize the risk of fraud or errors.
Step-by-step explanation:
The correct answer is c. Perform the shipping and billing function. The key segregation of duties for the revenue process is to ensure that different parties are responsible for different tasks to minimize the risk of fraud or errors. In this case, performing the shipping and billing function together would lack proper separation of duties as it combines the responsibility of two critical tasks. The other options, a, b, and d, involve separating tasks such as preparing shipping orders and bills of lading, performing credit and billing functions, and receiving cash and adjusting accounts receivable, which are necessary for effective segregation of duties.