To solve this question, the user needs to have a basic understanding of the software development life cycle. The requirement phase is a crucial phase in the software development process, and it serves several purposes.

Option A: To freeze requirements - This option is partially correct, as one purpose of the requirement phase is to document and finalize the requirements for the software. However, the term "freeze" may be misleading, as requirements are subject to change throughout the development process, and the requirement phase may need to be revisited if changes are made.

Option B: To understand user needs - This option is correct. During the requirement phase, developers work closely with stakeholders to gain a deep understanding of the user's needs, the problem the software is meant to solve, and the desired outcomes.

Option C: To define the scope of the testing - This option is incorrect, as the requirement phase is focused on defining the scope of the software development project, not the testing phase.

Option D: All of the above - This option is correct, as the requirement phase serves multiple purposes, including documenting and finalizing requirements, understanding user needs, and defining the scope of the software project.

Therefore, the answer is: D. All of the above.