A computer forensic audit is a process of collecting, preserving, analyzing, and presenting digital evidence from electronic devices in a legally admissible manner. It is most relevant in situations where data loss due to hacking of servers occurs, as it can help to identify the source, method, and extent of the attack, as well as recover the lost or damaged data. The other options are not as suitable for a computer forensic audit, as they relate to internal control issues, data quality issues, or system maintenance issues, which can be addressed by other types of audits or reviews. References: CISA Review Manual (Digital Version), Domain 4: Information Systems Operations and Business Resilience, Section 4.5 Computer Forensics1

The best option to provide an IS auditor assurance that the interface between a point-of-sale (POS) system and the general ledger is transferring sales data completely and accurately is A. Electronic copies of customer sales receipts are maintained. Electronic copies of customer sales receipts are records of the transactions that occurred at the POS system, which can be compared with the data transferred to the general ledger. This can help detect any errors, omissions, or discrepancies in the data transfer process and ensure that the sales data is complete and accurate.
The other options are not as effective as A in providing assurance that the interface between the POS system and the general ledger is transferring sales data completely and accurately. B. Monthly bank statements are reconciled without exception. Monthly bank statements are records of the cash inflows and outflows of the organization, which may not match with the sales data recorded by the POS system and the general ledger.
For example, there may be delays, discounts, returns, or refunds that affect the cash flow but not the sales revenue. Therefore, reconciling monthly bank statements without exception does not necessarily mean that the sales data is complete and accurate. C. Nightly batch processing has been replaced with real-time processing. Nightly batch processing is a method of transferring data from the POS system to the general ledger in batches at a scheduled time, usually at night. Real-time processing is a method of transferring data from the POS system to the general ledger as soon as the transactions occur. Real-time processing may improve the timeliness and efficiency of the data transfer process, but it does not guarantee that the sales data is complete and accurate. There may still be errors, omissions, or discrepancies in the data transfer process that need to be detected and corrected. D. The data transferred over the POS interface is encrypted.
Encryption is a process of transforming data into an unreadable form using a secret key or algorithm, so that only authorized parties can access the original data. Encryption protects the confidentiality and security of the data transferred over the POS interface, but it does not ensure that the sales data is complete and accurate.
There may still be errors, omissions, or discrepancies in the data transfer process that need to be detected and corrected.
References:
* ISACA, CISA Review Manual, 27th Edition, 2019, p. 2471
* ISACA, CISA Review Questions, Answers & Explanations Database - 12 Month Subscription2
* Sales Audit Overview - Oracle3
* Notes on Audit of Ledgers - Guidelines to Auditors - Accountlearning

Hash totals are a control technique used to ensure data integrity during batch processing. A hash total is a calculated value based on the data in a batch. This value is compared to a pre-calculated hash total to confirm that all data has been processed correctly and without alteration.
References
ISACA CISA Review Manual (27th Edition): Hash totals are discussed within the context of batch processing controls.
Other Auditing Resources: Hash totals are a fundamental control technique discussed in various audit and information security publications.

The expected costs for recovering the business would be used when performing a business impact analysis (BIA). A BIA is a process of identifying and evaluating the potential effects of disruptions to critical business functions or processes. A BIA helps to determine the recovery priorities, strategies, and resources needed to resume normal operations after a disruption. One of the key outputs of a BIA is an estimate of the financial losses or costs associated with different types of disruptions, such as lost revenue, increased expenses, contractual penalties, or regulatory fines.

The best document for an IS auditor to use in detecting a weakness in segregation of duties is a process flowchart. A process flowchart is a diagram that illustrates the sequence of steps, activities, tasks, or decisions involved in a business process. A process flowchart can help detect a weakness in segregation of duties by showing who performs what actions or roles in a process, and whether there is any overlap or conflict of interest among them. The other options are not as useful as a process flowchart in detecting a weakness in segregation of duties, as they do not show who performs what actions or roles in a process. A system flowchart is a diagram that illustrates the components, functions, interactions, or logic of an information system. A data flow diagram is a diagram that illustrates how data flows from sources to destinations through processes, stores, or external entities. An entity-relationship diagram is a diagram that illustrates how entities (such as tables) are related to each other through attributes (such as keys) in a database. References: CISA Review Manual (Digital Version), Chapter 3, Section 3.2