The first step to successfully implement a corporate data classification program is to approve a data classification policy. A data classification policy is a document that defines the objectives, scope, principles, roles, responsibilities, and procedures for classifying data based on its sensitivity and value to the organization. A data classification policy is essential for establishing a common understanding and a consistent approach for data classification across the organization, as well as for ensuring compliance with relevant regulatory and contractual requirements.

Selecting a data loss prevention (DLP) product (option B) is not the first step to implement a data classification program, as it is a technical solution that supports the enforcement of the data classification policy, not the definition of it. A DLP product can help prevent unauthorized access, use, or disclosure of sensitive data by monitoring, detecting, and blocking data flows that violate the data classification policy. However, before selecting a DLP product, the organization needs to have a clear and approved data classification policy that specifies the criteria and rules for data classification.

Confirming that adequate resources are available for the project (option C) is also not the first step to implement a data classification program, as it is a project management activity that ensures the feasibility and sustainability of the project, not the design of it. Confirming that adequate resources are available for the project involves estimating and securing the necessary budget, staff, time, and tools for implementing and maintaining the data classification program. However, before confirming that adequate resources are available for the project, the organization needs to have a clear and approved data classification policy that defines the scope and objectives of the project.

Checking for the required regulatory requirements (option D) is also not the first step to implement a data classification program, as it is an input to the development of the data classification policy, not an output of it. Checking for the required regulatory requirements involves identifying and analyzing the applicable laws, regulations, standards, and contracts that govern the protection and handling of sensitive data. However, checking for the required regulatory requirements is not enough to implement a data classification program; the organization also needs to have a clear and approved data classification policy that incorporates and complies with those requirements.

Therefore, option A is the correct answer.