Answer:
b) an electoral realignment
An electoral realignment occurs when one party replaces another party that has dominated national politics for a lengthy period of time.
Step-by-step explanation:
An electoral allignment occurs when a new party supplants the ruling party.Voting patterns are changes by some critical issue, event, or leader and remain changed for an extended period of time (maybe decades).
Punctuating each party era is a critical election - new coalitions form. Realignments occur roughly every thirty years (the displacement of a majority party by the minority party). It is caused by new issues or new voters.
Hence option b) an electoral realignment is the right option