The correct answer is A) democratic republic.
The United States is an example of the governmental system called a democratic republic.
The United States is a Republic formed by many states, called the states of the Union. There is a Constitution that allows citizens to vote and elect their representants in the legislative branch that has two chambers, the House of Representatives and the Senate. They also elect their President for a 4-year term with the possibility of reelection. And there also exist the judicial power represented by the US Supreme Court.
