Generally accepted standards of audit field work require that auditors obtain sufficient appropriate evidential matter to afford a reasonable basis for an opinion regarding the financial statements under examination. In considering what constitutes sufficient appropriate evidential matter, a distinction should be made between underlying accounting data and all corroborating information available to the auditor.

Required:
What presumptions can be made about each of the following:
a. The relative appropriateness of evidence obtained from external and internal sources.
b. The role of internal control with respect to internal evidence produced by an auditee’s data processing system.
c. The relative persuasiveness of auditor observation and recalculation evidence compared with the external, external-internal, and internal documentary evidence.