The correct answer is "Charlemagne crowned Holy Roman emperor, 800 CE."
The event that belongs in place C on the timeline is "Charlemagne crowned Holy Roman emperor, 800 CE."
In one of the most important events of that time, the pope Leo III crowned Charlemagne as the New Emperor of the Roman Empire. The exact date, December 25, 800 CE. Charlemagne was the King of the Frankish and was the one who could exert the leadership and influence to calm down the situation in Rome. One of the first things Charlemagne did was to improve the education conditions in the Empire.
The answer is the North Vietnamese took over the South Vietnam spreading communism Southward and this proved the domino theory (if one country come under the influence of communism, the surrounding countries would follow).
