In The Spirit of the Laws, Montesquieu proposed a division of power within the government between the legislative, the executive and the judiciary. 

The correct answer is option 'C', which is "The Spirit of Laws".

The Spirit of Laws, or in its original French title De l'esprit des lois, is a book written by Charles-Louis de Secondat, Baron de La Brède et de Montesquieu, commonly known as Montesquieu. It was published in 1748 and is considered one of the most influential works in the field of political science and jurisprudence.

The main themes explored in The Spirit of Laws are the separation of powers, the nature of governments, and the principles of political liberty. Montesquieu believed that the best way to prevent tyranny and protect individual liberty was to divide political power among different branches of government. He argued that a government should be structured in a way that balances power and prevents any one person or group from becoming too powerful.

Montesquieu proposed the concept of the separation of powers, which refers to the division of government into three separate branches: the legislative, executive, and judicial. Each branch has its own distinct powers and responsibilities, and they are meant to serve as checks and balances on each other. This idea greatly influenced the formation of modern democratic systems, including the United States Constitution.

In addition to the separation of powers, Montesquieu also discussed the different forms of government and their characteristics. He classified governments into three main types: republics, monarchies, and despotisms. He analyzed their strengths and weaknesses and argued that the best form of government depends on the specific circumstances of a society.

The Spirit of Laws also delves into various other topics such as climate and its impact on political systems, the role of religion in government, and the importance of customs and traditions in shaping a society's laws and norms. Montesquieu's ideas challenged the prevailing notions of his time and laid the foundation for modern political thought.

Overall, The Spirit of Laws is a seminal work that explores the principles of political science, the separation of powers, and the nature of governments. It continues to be highly regarded for its insights into the principles of liberty, the rule of law, and the importance of a well-structured government.