Which of the following statements about internal control is correct?
A. A properly maintained system of internal control reasonably ensures that collusion among employees cannot occur.
B. The establishment and maintenance of a system of internal control is an important responsibility of the external auditor.
C. An exceptionally strong system of internal control is enough for the auditor to eliminate substantive tests on a significant account balance.
D. The cost-benefit relationship is a primary criterion that should be considered in designing a system of internal control.