Final answer:
If you are a member of the Republican party and you go to vote for the party nominee for president, and on your ballot are candidates for both the Democratic and Republican nominations, you are most likely in an open primary election.
Step-by-step explanation:
If you are a member of the Republican party and you go to vote for the party nominee for president, and on your ballot are candidates for both the Democratic and Republican nominations, you are most likely in an open primary election. In an open primary, all voters, regardless of party affiliation, are allowed to vote. This means that as a Republican, you have the option to vote for either a Republican or Democratic candidate.