Which of the following statements about tests of controls is most accurate?

a. Auditing procedures cannot concurrently provide both evidence of the effectiveness of internal control procedures and evidence required for substantive tests.

b. Tests of controls include observations of the proper segregation of duties.

c. Tests of controls provide direct evidence about monetary misstatements in transactions.

d. Tests of controls ordinarily should be performed as of the balance sheet date or during the period subsequent to that date.