$1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16$

$5$n

Which of the following statements about internal coptrol 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.