B. Choice A misstates the complete diversity rule.
Defendants can be from the same state.
The complete diversity rule comes from the Court's interpretation of the statutory limits placed by Congress, not from the Constitution. In our American system attorneys are usually not recoverable against the other side, but when they are, they can count for jurisdictional amount. Also, attorneys fees are also not the same things as costs. Therefore even unrelated claims can be aggregated by a single plaintiff against a single defendant to satisfy jurisdictional amount. More than one plaintiff is attempting to come into federal court by aggregating the plaintiffs' claims together against a single defendant.