I think the answer is (b)
It is a legal concept that the state has the right to repeal, or nullify, any union law that the state treats as unconstitutional in relation to the Constitution of the United States.
John C. Calhoun, Andrew Jackson's vice-president and a native of South Carolina, suggested this idea.
<h3>Hope it helps!</h3>
The answer is b, the destruction of the Berlin wall.
A would be the correct answer!
