Serfs were freed in Eastern Europe during this time, although not necessarily due to economic modernization. All options are correct except option B.
The process of abolishing serfdom was one of the major transformations in Eastern Europe during this time. So the answer must be related to the abolishment of serfdom.
A. Most nations developed constitutional monarchies: This statement is not specific enough to be considered true or false for all Eastern European nations. While some nations did move towards constitutional monarchies, others did not.
B. Serfs were freed as economies became more modern: This statement is partially true. Serfdom was indeed abolished in many Eastern European countries during this time, but it wasn't necessarily due to the modernization of economies. In many cases, political and social factors played a more significant role.
C. Nobles were able to take power from Eastern European monarchs: This statement is generally false. While there were instances of Nobles gaining power, they didn't necessarily take it from monarchs. In most cases, the power dynamics between monarchs and nobles remained relatively stable, or monarchs even consolidated their power.
D. Serfdom was reimposed on peasants: This statement is false. Serfdom was abolished, not reimposed, in Eastern Europe during this time.
Therefore, the most accurate statement is B. Serfs were freed as economies became more modern. While not entirely accurate, it reflects the general trend of serfdom's abolition during this period.