The best description of the purpose of the U.S. Constitution from the options provided is:
B. it outlines how the government should make laws.
The U.S. Constitution establishes the framework for the federal government, including the legislative process, the roles of the different branches of government, and the relationship between the federal government and the states. While it does include protections for individual rights (such as those in the Bill of Rights), its primary purpose is to structure the government and define its powers.