The correct answer is:
C. He recorded public and historical events with much candor.
Explanation:
1. Samuel Pepys's diary became popular because he recorded public and historical events with great honesty and openness.
2. His detailed and candid accounts of significant events such as the Great Fire of London and the plague outbreak in London provided valuable insights into the historical context of the time.
3. Pepys's diary is considered an important historical document due to its accurate and vivid descriptions of the events he witnessed.
4. While his writing style was engaging, it was primarily the content of his diary that made it popular among readers interested in gaining a deeper understanding of the historical events of his era.