When Does a Referendum Take Place

When does a referendum take place?

A) When Congress rejects a law passed by a state legislature
B) When the U.S. Supreme Court rejects a law because it violates the U.S. Constitution
C) When the president refers his budget plan to Congress before the start of a fiscal year
D) When a state legislature refers an act of legislation to the voters for approval or disapproval
E) When voters choose the candidates who will represent their political party