The key here is recognising which term describes a threshold question decided ahead of the rest of the suit.
Since the facts describe sequencing within the same suit rather than a bar arising from another proceeding, the correct answer is Preliminary issue.
Thinking about why a court would want to decide one issue before allowing discovery clarifies the answer.
The efficiency-driven purpose of deciding a threshold question first, before allowing or refusing discovery, is what a preliminary issue is for.
Therefore, the correct answer is Preliminary issue.