One of the first steps of a project is to identify the stakeholders and their interests. Stakeholders are the individuals or groups who have an interest or influence in the project or its outcome. Identifying the stakeholders and their interests helps to understand their needs, expectations, roles, responsibilities, and communication preferences. It also helps to manage their involvement and engagement throughout the project life cycle, and to address any potential conflicts or issues that may arise. The other options are not the first steps of a project. Identifying the classes of users and their requirements is part of the requirements elicitation process, which occurs after the project initiation phase. Aligning the sponsor expectations along the project goals is part of the project charter development, which is also done after the project initiation phase.
Evaluating the sources for requirements and prioritizing them is part of the requirements analysis process, which occurs after the requirements elicitation process. References: PMI-PBA Examination Content Outline, page 10; PMI-PBA Reference List, page 1, BABOK Guide v3, page 50; 3.