In a RAO model, which stands for Responsible, Accountable, Consulted, and Informed, the accountable role must be assigned to only one individual. The accountable role is the person who has the ultimate authority and responsibility for the outcome of the project or task, and who approves or rejects the work done by the responsible role. The accountable role cannot be delegated or shared, as it is essential to have a clear and single point of accountability for each project or task.
The other roles can be assigned to more than one individual:
Responsible. This is the person who does the work or performs the task. There can be multiple responsible roles for different aspects or phases of a project or task, as long as they are coordinated and supervised by the accountable role.
Informed. This is the person who needs to be notified or updated about the progress or results of the project or task. There can be multiple informed roles who have an interest or stake in the project or task, but who do not need to be consulted or involved in the decision-making process.
Consulted. This is the person who provides input, feedback, or advice on the project or task. There can be multiple consulted roles who have expertise or experience relevant to the project or task, but who do not have the authority or responsibility to approve or reject the work done by the responsible role.

The most assurance over the completeness and accuracy of loan application processing with respect to the implementation of a new system can be obtained by running historical transactions through the new system.
Historical transactions are transactions that have been processed and recorded by the old system in the past.
Running historical transactions through the new system can provide the most assurance over the completeness and accuracy of loan application processing, bycomparing the results and outputs of the new system with those of the old system, and verifying whether they match or differ. This can help identify and resolve any errors or issues that may arise from the new system, such as data conversion, functionality, compatibility, etc.
Comparing code between old and new systems is a possible way to obtain some assurance over the completeness and accuracy of loan application processing with respect to the implementation of a new system, but it is not the most effective one. Code is a set of instructions or commands that define how a system operates or functions. Comparing code between old and new systems can provide some assurance over the completeness and accuracy of loan application processing, by checking whether the logic, algorithms, or functions of the new system are consistent or equivalent with those of the old system. However, this may not be sufficient or reliable, as code may not reflect the actual performance or outcomes of the system, and may not detect any errors or issues that may occur at the data or user level. Reviewing quality assurance (QA) procedures is a possible way to obtain some assurance over the completeness and accuracy of loan application processing with respect to the implementation of a new system, but it is not the most effective one. QA procedures are steps or activities that ensure that a system meets its quality standards and requirements, such as testing, verification, validation, etc. Reviewing QA procedures can provide some assurance over the completeness and accuracy of loan application processing, by evaluating whether the new system has been properly tested and verified before implementation. However, this may not be adequate or accurate, as QA procedures may not cover all aspects or scenarios of loan application processing, and may not reveal any errors or issues that may arise after implementation. Loading balance and transaction data to the new system is a possible way to obtain some assurance over the completeness and accuracy of loan application processing with respect to the implementation of a new system, but it is not the most effective one. Balance and transaction data are data that reflect the status and history of loan applications in a system, such as amounts, dates, payments, etc. Loading balance and transaction data to the new system can provide some assurance over the completeness and accuracy of loan application processing, by transferring data from the old system to the new system and ensuring that they are consistent and correct. However, this may not be enough or valid, as balance and transaction data may not represent all aspects or features of loan application processing, and may not indicate any errors or issues that may arise

An IT steering committee is a group of senior executives and stakeholders who provide strategic direction, guidance, and oversight for the IT function of an organization. An IT steering committee can help to improve the maturity of the IT team by ensuring that the IT initiatives are aligned with the business goals and objectives, that the IT resources are allocated and utilized effectively and efficiently, and that the IT performance and value are measuredand communicated. An IT steering committee can also help to resolve conflicts, prioritize demands, and foster collaboration among the IT project managers and other business units.
References
ISACA CISA Review Manual, 27th Edition, page 254
Auditing IT Governance
The Impact of Poor IT Audit Planning and Mitigating Audit Risk
IS Audit Basics: The Components of the IT Audit Report

In the development of a new financial application, the IS auditor's first involvement should be in the feasibility study. A feasibility study is a preliminary analysis that evaluates the technical, operational, economic, and legal aspects of a proposed project or system. A feasibility study helps determine whether the project or system is viable, feasible, and desirable for the organization and its stakeholders.
The IS auditor's role in the feasibility study is to provide an independent and objective assessment of the project or system's risks, benefits, costs, and impacts. The IS auditor should also ensure that the feasibility study follows a structured and systematic approach, considers all relevant factors and alternatives, and complies with the organization's policies and standards. The IS auditor should also verify that the feasibility study is documented and communicated to the appropriate decision-makers.
The IS auditor's involvement in the feasibility study is important because it can help:
Identify and mitigate potential risks and issues that could affect the project or system's success Evaluate and justify the project or system's alignment with the organization's strategy, goals, and value proposition Estimate and optimize the project or system's resources, budget, schedule, and quality Assess and enhance the project or system's security, reliability, performance, and usability Ensure that the project or system meets the expectations and requirements of the users and other stakeholders The other three options are not the first involvement of the IS auditor in the development of a new financial application, although they may be part of the subsequent stages of the development process. Control design is the process of defining and implementing controls that ensure the security, integrity, availability, and efficiency of the system. Application design is the process of specifying the functional and technical features of the system. System test is the process of verifying that the system meets the specifications and requirements.
Therefore, feasibility study is the best answer.
References:
[Feasibility Study - ISACA]
[IS Auditing Guideline G13 Performing an IS Audit Engagement - ISACA]