Concerning internal control, which one of the following statements is correct? Explain.

a. Broadly speaking, an internal control structure is only necessary in large organizations.

b. The purposes of internal control are to check the accuracy of accounting data, safeguard assets against theft, promote efficiency of operations, and ensure that management's policies are being followed.

c. Once an internal control structure has been established, it should be effective as long as the formal organization remains unchanged.

d. An example of internal control is having one employee count the day's cash receipts and compare the total with the total of the cash register tapes.