The main objective of the Constitution of 1791 was to establish a constitutional monarchy in France. This marked a significant change in the political system of the country, as it aimed to limit the powers of the king and establish a system based on a written constitution.

**Background:**
Before the Constitution of 1791, France was an absolute monarchy, where the king held supreme power and there were no checks on his authority. However, the French Revolution of 1789 brought about significant political and social changes, leading to the overthrow of the monarchy.

**Establishing a Constitutional Monarchy:**
The Constitution of 1791 aimed to create a constitutional monarchy, which would limit the powers of the king and establish a system of government based on a constitution. This meant that the king would no longer have absolute authority and would be subject to the laws and regulations outlined in the constitution.

**Limiting the Powers of the King:**
One of the key objectives of the constitution was to limit the powers of the king. It sought to establish a separation of powers, where the king would share power with the legislative assembly and the judiciary. This would ensure a system of checks and balances, preventing any one branch of government from becoming too powerful.

**Protection of Individual Rights:**
The Constitution of 1791 also aimed to protect the rights of individuals. It guaranteed certain fundamental rights, such as freedom of speech, religion, and the press. These rights were considered essential in establishing a fair and just society, where individuals had the freedom to express themselves and practice their religion without fear of persecution.

**Abolition of Feudal Privileges:**
Another important objective of the Constitution of 1791 was to do away with feudal privileges. Feudalism was a social system that granted certain privileges and rights to the nobility and clergy, while the common people were subjected to various forms of oppression and exploitation. The constitution aimed to abolish these privileges and establish a more egalitarian society.

In conclusion, the main objective of the Constitution of 1791 was to establish a constitutional monarchy, limit the powers of the king, protect individual rights, and abolish feudal privileges. This marked a significant shift in the political system of France, laying the foundation for a more democratic and egalitarian society.

The correct answer is 'a' = according to the book of page no 10