The first step that the CIO should do to help ensure continuous alignment of IT with the new business strategy is to review the existing IT strategy against the new business strategy. A review is a process of evaluating and comparing the current state and performance of the IT strategy with the desired state and expectations of the new business strategy. A review can help identify the strengths, weaknesses, opportunities, and threats of the IT strategy, as well as the gaps, risks, and issues that need to be addressed. A review can also provide insights and recommendations for improving and aligning the IT strategy with the new business strategy. According to COBIT 5, one of the seven enablers of IT governance is performance management, which includes reviewing and monitoring the achievement of IT-related goals and objectives1. The review is also part of the IT governance domain 2: Strategic Alignment2.
The other options are not the first steps that the CIO should do to ensure continuous alignment of IT with the new business strategy. Revising the existing IT strategy to align with the new business strategy is a step that follows after reviewing the existing IT strategy, as it involves making changes and adjustments to the IT strategy based on the findings and recommendations of the review. Establishing a new IT strategy committee for the new enterprise is a step that may or may not be necessary depending on the existing governance structure and processes, and it does not directly address the alignment issue. Assessing the IT cultural aspects of the acquired entity is a step that may be relevant for integrating and harmonizing the IT functions and practices of both entities, but it does not ensure alignment with the new business strategy. References := 1:
COBIT 5: A Business Framework for the Governance and Management of Enterprise IT, ISACA, page 312:
CGEIT Review Manual 2023, ISACA, page 69.

Senior management regularly reviewing the IT portfolio is the best IT governance practice to support IT and enterprise strategic alignment, because it helps to ensure that the IT investments are aligned with the business strategy and goals, and that they deliver value to the enterprise. An IT portfolio is a collection of IT projects, programs, services, and assets that support the business objectives and processes of an organization1. Senior management regularly reviewing the IT portfolio helps to prioritize, monitor, and evaluate the IT investments based on their performance, benefits, costs, and risks2. It also helps to identify and address any gaps, issues, or opportunities for improvement in the IT portfolio2. Senior management regularly reviewing the IT portfolio also helps to communicate and collaborate with the IT department and other stakeholders, and to provide guidance and direction for the IT strategy and governance2.
References := IT Portfolio Management: A Simplified Guide | Planview, IT Governance - How to align IT and business strategy?

A cost-benefit analysis (CBA) is a process that's used to estimate the costs and benefits of projects or investments to determine their profitability for an organization. A CBA is a versatile method that's often used for business administration, project management and public policy decisions1. A CBA can help the CIO prioritize the improvement initiatives based on their expected value and feasibility, and justify the allocation of resources and funding for them. A CBA can also align the IT goals with the enterprise objectives and demonstrate the IT value delivery to the stakeholders2. References :=
2: CGEIT Exam Content Outline | ISACA
1: Cost-Benefit Analysis: A Quick Guide with Examples and Templates

This is because a portfolio review is a process of evaluating the performance and value of IT investments in relation to the business objectives and strategy. A portfolio review can help to identify the alignment, contribution, and optimization of IT investments, as well as the risks, issues, and opportunities for improvement. A portfolio review can also help to communicate and demonstrate the value of IT to the board and other stakeholders, as well as to support decision-making and prioritization of IT resources.
Some of the sources that support this answer are:
* 1: This source explains the value of IT governance and how it can help to optimize risk and manage resources to support the organization's mission, goals, and objectives. It also discusses some of the governance enablers, such as principles, processes, and policies, that can help to align IT with the business context.
* 2: This source provides a research-based methodology to improve IT governance and drive business results. It suggests that conducting a portfolio review is one of the steps to redesign the governance framework and ensure that IT investments are aligned with the business strategy and deliver value.
* 3: This source defines IT portfolio management as a discipline that enables organizations to manage their IT investments as a collection of projects, programs, and services that contribute to the enterprise's strategic goals. It also describes some of the benefits of IT portfolio management, such as improving alignment, optimizing value, reducing risk, and enhancing transparency.

Continuous monitoring provides the best assurance on the effectiveness of IT service management processes because it involves collecting, analyzing, and reporting data on the performance, quality, and outcomes of the IT services on an ongoing basis. Continuous monitoring helps to identify and address any issues, gaps, or deviations from the expected standards and goals of the IT service management processes. It also helps to measure and demonstrate the value and impact of the IT services to the customers and stakeholders. Continuous monitoring can also support continuous improvement and innovation of the IT service management processes by providing feedback and insights for decision-making and planning