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

a. Competence of evidential matter refers to the amount of corroborative evidence obtained.

b. The more effective the internal control, the more assurance it provides about the reliability of the accounting data and financial statements.

c. Information obtained indirectly from independent outside sources is more persuasive than the auditor's direct personal knowledge obtained through observation and inspection.

d. Competence of evidential matter refers to the audit evidence obtained from outside the entity.