In whatever it does, government must act fairly and in accord with established rules. It may not act unfairly, arbitrarily, or unreasonably.

B. right to privacy
A. separation of powers
D. social contract
C. due process

C. due process

The correct answer would be C. due process. Due process ensures that government actions are fair and in accordance with established rules. It prohibits unfair, arbitrary, or unreasonable actions by the government. The right to privacy (B) and separation of powers (A) are important principles in governance, but they are not directly related to the government acting fairly and in accordance with established rules. The social contract (D) is a concept that refers to the agreement between individuals and the government, but it does not specifically address the government's obligation to act fairly and within established rules.