Final answer:
The nonfiction genre that focuses on true accounts of past periods or events is c) Histories, which provide a wide-scale perspective and analysis of historical developments.
Step-by-step explanation:
The nonfiction genre that involves true accounts of only past periods or events is c) Histories. Unlike memoirs, autobiographies, or biographies that are centered around personal experiences of individuals and often written in a narrative style, histories are comprehensive examinations of past events and are typically aimed at presenting a wide-scale perspective on historical developments.
While a memoir is a personal account and may include specific anecdotes and memories, a history encompasses a broader analysis that isn't limited to the author's personal experiences. It is scholarly in nature, often includes a synthesis of primary and secondary sources, and seeks to provide insight and understanding into past societies, cultures, and occurrences.