The best recommendation to prevent unauthorized access to cloud-based applications and data is to implement multi-factor authentication (MFA). MFA is a method of verifying the identity of a user by requiring two or more pieces of evidence, such as a password, a code sent to a phone, or a biometric factor. MFA adds an extra layer of security to prevent unauthorized access, even if the user's password is compromised or stolen. MFA can also help comply with data privacy and security regulations, such as the General Data Protection Regulation (GDPR) and the Health Insurance Portability and Accountability Act (HIPAA).
The other options are not as effective as MFA in preventing unauthorized access. An intrusion detection system (IDS) is a tool that monitors network traffic and alerts administrators of suspicious or malicious activity, but it does not prevent access by itself. Updating security policies and procedures is a good practice, but it does not ensure that users follow them or that they are enforced. Utilizing strong anti-malware controls on all computing devices can help protect against malware infections, but it does not prevent users from accessing cloud-based applications and data from any Internet-connected web browser.
References:
* ISACA, CISA Review Manual, 27th Edition, 2019, p. 2471
* ISACA, CISAReview Questions, Answers & ExplanationsDatabase - 12 Month Subscription2
* What Is Cloud Security? | Google Cloud3
* 5 Cloud Application Security Best Practices | Snyk4

The best indicator of the effectiveness of an organization's incident response program is the financial impact per security event. This metric measures the direct and indirect costs associated with security incidents, such as loss of revenue, reputation damage, legal fees, recovery expenses, and fines. By reducing the financial impact per security event, the organization can demonstrate that its incident response program is effective in mitigating the consequences of security breaches and restoring normal operations as quickly as possible.
Number of successful penetration tests, percentage of protected business applications, and number of security vulnerability patches are indicators of the security posture of the organization, but they do not reflect the effectiveness of the incident response program. References: ISACA Journal Article: Measuring Incident Response Effectiveness

Asking management why the regulatory changes have not been included is the first thing that an IS auditor should do during the planning stage of a compliance audit. An IS auditor should inquire about the reasons for not updating the inventory of compliance requirements with recent regulatory changes related to managing data risk. This will help the IS auditor to understand whether there is a gap in awareness, communication, or implementation of compliance obligations within the organization. The other options are not the first things that an IS auditor should do, but rather possible subsequent actions that may depend on management's response. References:
* CISA Review Manual (Digital Version), Chapter 2, Section 2.31
* CISA Review Questions, Answers & Explanations Database, Question ID 214

A post-implementation review (PIR) is an assessment conducted at the end of a project cycle to determine if the project was indeed successful and to identify any existing flaws in the project1. One of the main objectives of a PIR isto evaluate the outcome and functional value of a project1. Therefore, an IS auditor should be most concerned with whether the system meets the intended requirements and delivers the expected benefits to the stakeholders. A system that does not have a maintenance plan is a major risk, as it may not be able to cope with changing needs, fix errors, or prevent security breaches. A maintenance planis essential for ensuring the system's reliability, availability, and performance in the long term2.
The other options are less critical for a PIR, as they are more related to the project management aspects than the system quality aspects. The system may contain several minor defects that do not affect its functionality or usability, and these can be resolved in future updates. The system deployment may be delayed by three weeks due to unforeseen circumstances or dependencies, but this does not necessarily mean that the system is faulty or ineffective. The system may be over budget by 15% due to various factors such as scope creep, resource constraints, or market fluctuations, but this does not imply that the system is not valuable or beneficial.
References: 1: Post-Implementation Review Best Practices - MetaPM 2: What is Post-Implementation Review in Project Management?