Which of the following statements concerning audit evidence is correct?

a. To be appropriate, audit evidence should be either persuasive or rel- evant but need not be both.

b. The measure of the reliability of audit evidence lies in the auditor's judgment.

c. The difficulty and expense of obtaining audit evidence concerning an account balance is a valid basis for omitting the test.

d. A client's general ledger may be sufficient audit evidence to support the financial statements.