Which of the following statements is generally correct about the competence of evidential matter?

a. The auditor’s direct personal knowledge, obtained through observation and inspection, is more persuasive than information obtained indirectly from inde¬ pendent outside sources.

b. To be competent, evidential matter must be either valid or relevant, but need not be both.

c. Accounting data alone may be considered sufficient competent evidential mat¬ ter to issue an unqualified opinion on financial statements.

d. Competence of evidential matter refers to the amount of corroborative evi¬ dence to be obtained.