Which of the following statements is TRUE regarding the financial statement audit by an external auditor?

a. Sampling techniques are not allowed by GAAS as they have not been verified as to producing audit-appropriate results.

b. Sampling techniques are inherent throughout much of the audit process.

c. Sampling techniques are approved by GAAS for use during substantive testing but not approved for use for test of controls purposes.

d. Sampling techniques are approved by GAAS for use when testing balance sheet accounts for audit purposes but not allowed when testing income statement accounts for audit purposes.