Answer: D(?)
Explanation: If you are trying to replace the phrase within the underlined sentence, then A, B, and C aren't good options for the sentence structure. Only D makes sense.
Federalism meaning power is shared between the national and state governments. Separation of powers into branches that make, enforce or interpret laws. Balance of Power - controls (checks) can be made on the other branches. Limited government - everyone is bound by the US Constitution.
C the alps provided protection