When a progressive tense is used in the independent clause, the dependent clause typically uses tense.
a. simple past
b. simple present
c. progressive past
d. progressive present

The answer would be a.  when a progressive tense is used in the independent clause, the dependent clause typically uses the simple past

A is the answer I think

Delegates: representatives who cast votes at a political party's national convention. binding: if a primary or caucus is “binding” that means the delegates won in that contest are legally bound to vote for a particular candidate at the parties national convention.a primary is a preliminary election used to determine a party's nominee for a specific office. the winner of the party's caucus, or primary, wins the party nomination for that state. then the delegates meet at their party's national party convention, which is a formal gathering of all party delegates from all states.