Which of the following is an example of a primary source?

A primary source is a direct or firsthand piece of evidence from the time period or event being studied. It provides original data or firsthand testimony and has not been altered or interpreted by others. An interview transcript fits this definition perfectly, as it captures the personal thoughts, experiences, and perspectives of the individual being interviewed, offering direct insight into their unique viewpoint.

In contrast, a textbook compiles information and interpretations from various sources, serving as a secondary source intended for educational purposes. Similarly, a biography, while based on original material, is a secondary source because it interprets and summarizes someone else's life story. A research article typically involves the analysis of existing data or information and often includes the authors' interpretations or conclusions, further categorizing it as a secondary source rather than a primary one.