Determining a client's eligibility and appropriateness for treatment occurs during the _________ process.

The process of determining a client's eligibility and appropriateness for treatment is best captured during the screening phase. Screening involves the initial gathering of information to identify whether an individual may have substance use issues and if they require further assessment for treatment. This process is crucial because it establishes the groundwork for understanding the client's needs and ensuring they are directed toward the most suitable level of care.

During screening, practitioners typically use standardized tools or questionnaires designed to assess the presence and severity of substance use issues. This helps in quickly identifying those who might benefit from further evaluation or treatment, allowing for efficient use of resources and guiding clients toward appropriate care options.

While assessment, evaluation, and admission are all important processes within the larger treatment continuum, they serve different purposes. Assessment usually involves a more in-depth exploration of the client's issues and can include a comprehensive clinical history, whereas admission relates to the formal acceptance of a client into a treatment program based on findings from previous steps. Thus, the screening phase is specifically focused on the initial eligibility and appropriateness for treatment, making it the correct answer.