Which primary source document could a historian understand why the civil war started?

A Charleston Mercury editorial published in 1860

Explanation:

Charleston Mercury editorial published in 186. a year before the beginning of the US Civil War, would be and ideal item for an historian trying to understand the situation in the US at that time. Newspaper articles are considered one of the primary sources that are used to study history. They represent evidence and testimony of a time long passed.  

i believe your answer is d)