A differential backup scheme is the best option when storage media is limited, as it only backs up the data that has changed since the last full backup. This reduces the amount of storage space required and also simplifies the restoration process, as only the last full backup and the last differential backup are needed. A real-time backup scheme would require continuous replication of data, which would consume a lot of storage space and network bandwidth. A virtual backup scheme would create a snapshot of the data at a point in time, but it would not reduce the storage space required, as it would still need to store the changes made to the data.
A full backup scheme would back up all the data every time, which would require the most storage space and also take longer to complete. References: ISACA, CISA Review Manual, 27th Edition, 2018, page 405

Consolidating mission-critical applications onto a single large server introduces a single point of failure. If the server experiences an outage, all hosted applications could be impacted simultaneously, leading to significant operational disruptions. While continuous monitoring costs, potential network bandwidth issues, and challenges in capacity forecasting are valid concerns, the risk of a single outage affecting multiple critical applications presents the most substantial threat to business continuity.
References:
* ISACA CISA Review Manual, 28th Edition, Chapter 4: Information Systems Operations and Business Resilience.

The most important control to assess in an audit of an organization's accounts payable processes is segregation of duties between issuing purchase orders and making payments. Segregation of duties is a principle that requires different individuals or departments to perform different tasks or functions within a process, in order to prevent fraud, errors, or conflicts of interest. In the accounts payable process, segregation of duties between issuing purchase orders and making payments ensures that no one person can initiate and complete a transaction without proper authorization and verification. This reduces the risk of duplicate payments, overpayments, unauthorized payments, or payments to fictitious vendors.
References:
* Accounts payable controls
* Accounts Payable Internal Controls: A Simple Checklist

Control totals are a method of verifying the accuracy and completeness of data processing by comparing the totals of key fields in input and output records1. Control totals can be used to reduce the risk of incomplete processing, which is the failure to process all the data or transactions that are expected or required2.
Incomplete processing can result in data loss, inconsistency, or incompleteness, which can affect the quality and reliability of the information system and its outputs. Incomplete processing can be caused by various factors, such as:
Hardware or software failures that interrupt the processing or transmission of data2 Human errors or omissions that skip or miss some data or transactions2 Malicious attacks or unauthorized access that delete or modify some data or transactions2 Environmental hazards or disasters that damage or destroy some data or transactions2 Control totals can help detect and prevent incomplete processing by:
Providing a benchmark or reference point to compare the input and output data or transactions1 Identifying any discrepancies or deviations from the expected or required totals1 Alerting the users or operators to investigate and resolve the causes of incomplete processing1 Ensuring that all the data or transactions are properly transmitted, converted, and processed1 The other options are not as relevant as control totals for reducing the risk of incomplete processing. Posting to the wrong record is the error of assigning or transferring data or transactions to an incorrect account, file, or record3. Improper backup is the failure to create, store, or restore copies of data or transactions in case of loss, corruption, or damage4. Improper authorization is the lack of proper permission or approval to access, modify, or process data or transactions. Control totals may not be able to prevent or detect these errors or failures, as they are not related to the completeness of data processing. Therefore, option B is the correct answer.
References:
control totals - Barrons Dictionary - AllBusiness.com
What is control total amount? - Sage Advice US
Posting Error Definition
Backup Definition
[Authorization Definition]