Which is the best source of historical evidence to learn about how an event unfolded

 C. A newspaper account written when the event occurred

Explanation:  Of the options offered, the best is newspapers account written when the event happened, i.e. occurred. Journals and newspaper articles written at the time of the events are among the primary sources, and in addition to them are letters, memos, testimonies, photographs, diaries, etc. Event news sources contain dates, all or most of the event information, facts, details descriptions, sequence, and usually contain the least bias, as would be the case with a political map which is one of the options offered. In addition, when printing an article about an event, there is less chance of mistake about some relevant information, as would be the case with eyewitness memory.