The correct answer is: (A) Yes, because there was incomplete diversity of citizenship.

For diversity jurisdiction to exist, all plaintiffs must have been diverse from all defendants at the time the suit is commenced. The first plaintiff was a citizen of State B when the case was filed, because that is the last state in which he resided with the intent to remain indefinitely. The defendant was also a citizen of State B because that was the location of its principal place of business. Without complete diversity of citizenship at the moment of filing, diversity jurisdiction did not exist and the court was required to dismiss the case.

(B) Incorrect. Yes, because the plaintiffs did not plead the amount in controversy with particularity.

In federal court, the amount in controversy does not have to be pled with particularity. Federal Rule of Civil Procedure 8 required the plaintiffs to make a demand for judgment, and they demanded in excess of $75,000. The complaint's allegations determined the amount in controversy unless it was clear to a legal certainty that the plaintiffs could not each recover in excess of $75,000. In a tort case with no statutory cap on damages, there was no such legal certainty.

(C) Incorrect. No, because the motion was filed too late.

The defense of lack of subject-matter jurisdiction is never waived, per Federal Rule of Civil Procedure 12(h)(3).

(D) Incorrect. No, because the first plaintiff resided in State A at the time the suit was filed.

The existence of complete diversity is determined by the citizenship of the parties at the time of commencement of the case, not by their residence. The first plaintiff resided in State A at the time of commencement of the case, but at all times had the intent to return to State B, the last place where he was domiciled. The first plaintiff was domiciled at all times, including the moment the case was commended, in State B, and was thus a citizen of State B when the case was filed, as was the defendant. As such, there was incomplete diversity.