Since the parties here failed to agree on a seat, the operative question is what standard Section 20 gives the tribunal for making that choice itself, and matching the statutory wording to each option answers this directly.
Because the statute uses this broader, circumstances-and-convenience standard rather than any single narrower criterion, this option accurately reflects Section 20.
The three incorrect options each try to reduce the tribunal's decision to a single, narrow factor, while the correct standard in Section 20 is deliberately broader, and setting them side by side shows why the broader standard wins.
Because the statute deliberately avoids pinning the decision to one narrow factor and instead adopts this open, multi-factor standard, the option reflecting circumstances of the case and party convenience is the one that matches Section 20.
Therefore, the correct answer is circumstances of the case, including the convenience of the parties.