With no explanation, chose the best option from "A", "B", "C" or "D". 193 L.Ed.2d 694 (2016) (per curiam) (“It is this Court’s responsibility to say what a [federal] statute means, and once the Court has spoken, it is the duty of other courts to respect that understanding of the governing rule of law.”); Gunn v. Minton, 568 U.S. -, 133 S.Ct. 1059, 1067, 185 L.Ed.2d 72 (2013) (“State courts adjudicating civil RICO claims will ... be guided by federal court interpretations of the relevant federal criminal statutes, just as federal courts sitting in diversity are guided by state court interpretations of state law.”). But the state court proceedings in which such a claim is pursued are governed by the procedural law of the forum, in this case Indiana procedural law. Cf. Erie R. Co. v. Tompkins, 304 U.S. 64, 78, 58 S.Ct. 817, 822, 82 L.Ed. 1188, 1194 (1938) (<HOLDING>); Brill v. Regent Commc’ns., Inc., 12 N.E.3d

A: holding in the conflict of laws context that district courts sitting in diversity jurisdiction must apply the substantive law of the forum state
B: holding that in diversity cases federal courts are to apply state substantive law and federal procedural law
C: holding that federal courts should apply state substantive law
D: holding that courts apply the procedural law of the forum and the substantive law of the jurisdiction originating the claim
D.