Final answer:
An example of constitutional law in the U.S. is the U.S. Constitution and its amendments, which detail the structure of the federal government and the rights of the people. The correct option is (A).
Step-by-step explanation:
An example of constitutional law in the U.S. legal system is A) The U.S. Constitution and its amendments, which establish the structure and powers of the federal government and the rights of the people. This includes the separation of powers into the three branches of government—legislative, executive, and judicial—as outlined in the first three articles of the Constitution. Furthermore, the Bill of Rights and subsequent amendments provide a framework of fundamental rights and liberties, such as freedom of speech and equal protection under the law.