Which of the following presumptions does not relate to the competence of audit evidence?

a) An auditor's opinion, to be economically useful, is formed within a reasonable time and based on evidence obtained at a reasonable cost.

b)The independent auditor's direct personal knowledge, obtained through observation and inspection, is more persuasive than information obtained indirectly.

c) Evidence obtained from independent sources outside the entity is more reliable than evidence secured solely within the entity.

d) The more effective the internal control structure, the more assurance it provides about the accounting data and financial statements.