参考答案：International Standards on AuditingInternational Standards on Auditing (ISAs) are issued by the International Auditing and Assurance Standards Board (IAASB) and provide guidance on the performance of an audit.ISAs only apply to the audit of historical financial information. They are written in the context of an audit of financial statements by an independent auditor.The ISAs contain basic principles and essential procedures together with related guidance in the form of explanatory material and appendices. It is necessary to consider and understand the entire text of an ISA to understand and apply the basic principles and essential procedures.The basic principles and essential procedures of an ISA are to be applied in all cases. If in exceptional cases the auditor deems it necessary to depart from an ISA to achieve the overall aim of the audit, then this departure must be justified.