Answer:
1 - a. The people of France would be unable to trust each other enough to create a stable democracy.
This is actually what happened. Robespierre's Reign of Terror, and the Committee of Public Safety created an very negative enviroment in which people distrusted each other, and friends became enemies. This contributed to the failures of the revolution and the ascent of power of Napoleon.
2 - a. A republic requires a a group of representatives elected by citizens.
Ancient Athenian Democracy was a form of direct democracy in which a few citizens met to discuss public matters. The Republicanism that the Enlightenment philosophers promoted was different: it argued for a larger representation of the people through elected representatives elected by citizens in a legislative body.
3 - b. Popular sovereignty is the idea that a country's leader rules by permission of a majority of that country's citizens.
Popular sovereignty is the idea that the power of government stems from the people, and that the people have the right to change or overthrow a government when people feel that the government is acting against their interest. This idea is enshrined in the U.S. Constitution to this day.