The first task that an IS auditor should complete during the preliminary planning phase of a database security review is to determine which databases will be in scope. The scope defines the boundaries and objectives of the audit, as well as the resources, time, and budget required. The IS auditor should identify the databases that are relevant to the audit based on factors such as their criticality, risk, complexity, size, type, location, and ownership. The IS auditor should also consider the regulatory, contractual, and organizational requirements that apply to the databases. By defining the scope clearly and accurately, the IS auditor can ensure that the audit is focused, feasible, and effective. References:
CISA Review Manual (Digital Version)
CISA Questions, Answers and Explanations Database

Team member assignments based on individual competencies is the most important factor to meet the IS audit standard for proficiency. Proficiency is the ability to apply knowledge, skills and experience to perform audit tasks effectively and efficiently. The IS audit standard for proficiency requires that IS auditors must possess the knowledge, skills and discipline to perform audit tasks in accordance with applicable standards, guidelines and procedures. Team member assignments based on individual competencies is a way to ensure that each IS auditor is assigned to audit tasks that match their level of proficiency, and that the audit team as a whole has sufficient and appropriate proficiency to conduct the audit. The other options are not as important as option C, as they do not ensure that the IS auditors have the required proficiency to perform audit tasks.
Having a globally recognized audit certification is a way to demonstrate proficiency in IS auditing, but it does not guarantee that the IS auditor has the specific knowledge, skills and experience needed for a particular audit task or system. Technical co-sourcing is a way to supplement the proficiency of the IS audit team by hiring external experts or consultants to perform certain audit tasks or functions, but it does not replace the need for internal IS auditors to have adequate proficiency. Having a supervisor review the new auditors' work is a way to ensure quality and accuracy of the audit work, but it does not ensure that the new auditors have the necessary proficiency to perform audit tasks independently or competently. References: CISA Review Manual (Digital Version) , Chapter 1: Information Systems Auditing Process, Section 1.4: Audit Skills and Competencies.