For any given audit, there are many ways in which the auditor can gather evidence to achieve the audit's overall objective of providing an opinion on the financial statements.
There are two primary considerations influencing the approach an auditor chooses: (i) sufficient appropriate evidence must be collected to meet the auditor's professional responsibility, and (ii) the cost of compiling evidence must be kept to a minimum.

a. Discusses how auditors can balance these two considerations?
B. Give three examples of relatively reliable documents and three examples of less reliable documents. What are the characteristics that distinguish the two?
c. Explain why external evidence is more reliable than internal evidence.