In Jury Trials, the Degree of Proof Referred to as Beyond

In jury trials, the degree of proof referred to as beyond a reasonable doubt:

A) is the degree required in both criminal and civil cases.
B) is a rule of evidence but has not been made applicable to the states by the due process clause.
C) does not have to be explained by the trial judge in a jury instruction in every criminal case.
D) must, according to the U.S. Supreme Court, always be defined when the charge is made to the jury.