Final answer:
People primarily write diaries to understand themselves and others, and to keep a record of events in their lives, rather than to showcase intelligence or provide an unbiased perspective on events.
Step-by-step explanation:
People write diaries for various personal reasons. Contrary to option (A), which suggests writing diaries to showcase intelligence, this is not commonly the primary intent. Diaries are not typically written to provide an unbiased perspective (option B); rather, they reflect the very personal and subjective experience of the writer.
Most accurately, diaries serve as a means for individuals to understand themselves and others (option C), as well as to maintain a record of events in their lives (option D). This personal writing practice allows one to share meaningful experiences, reflect on them, and potentially connect with others. However, it is essential to acknowledge that diaries, being personal narratives, can present the writer in a certain light and may not be entirely free of bias or self-promotion.