Final answer:
A (D) runoff primary occurs when no candidate achieves a majority in the first election round, prompting a second round between the top two candidates to determine the winner.
Step-by-step explanation:
The scenario presented involves a runoff primary, which is a special type of primary election used when no candidate wins a majority of the votes in the first round of voting. In a runoff primary, the top two candidates, regardless of party affiliation, face off in a second round to determine the winner.
Unlike closed primaries, where only registered party members can vote, or open primaries, which allow any registered voter to participate, a runoff is specifically for settling undecided elections where no single candidate has achieved a majority.
This is common in a majority election system, where a candidate must secure over 50 percent of the votes to win. It is also important to note that when discussing primaries, some states in the U.S. may use the top-two primary method, where all candidates are listed on a single ballot regardless of party, and the two with the most votes proceed to the general election.