In Erie Railroad Co

In Erie Railroad Co. v. Tompkins, where Tompkins sued a New York company that owned a train that hit him in Pennsylvania:

A) the U.S. Supreme Court said that state common law must be applied in federal court
B) the U.S. Supreme Court said that federal common law must be applied in federal court
C) the U.S. Supreme Court said that since this was a matter of common law involving two states, it was a matter for the state courts, not federal district court
D) the Supreme Court of Pennsylvania said this was a matter of New York common law that must be tried in federal court
E) the Supreme Court of New York said this was a matter of Pennsylvania common law that must be tried in that state