Which ONE of the following is NOT a type of primary election?

The selection of "plural primary" as not being a type of primary election is accurate. In the context of American electoral processes, the established types of primary elections include closed primaries, open primaries, and direct primaries.

A closed primary allows only registered party members to vote in their party’s primary election, ensuring that only those who are affiliated with a party can help choose its nominee. An open primary allows any registered voter, regardless of party affiliation, to participate in the primary election of any party. A direct primary is a system where voters directly select the candidates who will run for public office in the general election, typically utilized to give a more democratic approach to candidate selection.

The term "plural primary" does not correspond with these recognized forms of primary elections in governing practice, which makes it the correct choice when identifying the option that does not belong.