Final answer:
A fundamental principle of American democracy according to the information provided is the balance between individual rights and state powers (option C) , often realized through Federalism which permits a balance of national and state government authorities.
Step-by-step explanation:
According to Justice William Brennan, a fundamental principle of American democracy is the protection and importance of individual rights and liberties over the powers of the state. This principle aligns with the idea of constitutionalism, which emphasizes that a government's authority comes from a set of political values and norms derived from a country's constitution and is balanced by the fundamental worth of each individual. This is in harmony with the Fourteenth Amendment, which includes the Equal Protection Clause, mandating that state governments treat all people the same, and underpins the notion that all people should enjoy equal status and moral worth.
The correct answer to the student's question is not directly provided in the provided sources, but based on the emphasis on balance between individual rights and state power, constitutionalism and the pursuit of happiness, the principle that most resonates with Justice William Brennan's views is likely to be 'Federalism' (Option A), as it is the structure that allows for both a national government and state governments, each with their own rights and powers, which in turn helps to ensure a balance between individual liberties and the government's powers. However, without the direct reference to Justice William Brennan's statements, this answer is a best-educated guess based on the principles described.