Able sues Baker for breach of written contract in federal court. At trial, Able testifies. On cross-examination, Baker's counsel asks Able to disclose what he told his attorney about the contract's terms. Abel's counsel objects on privilege grounds. What law will a judge apply to resolve the issue? 

 a) Federal common law. 

b) The Federal Rules of Evidence. 

c) State privilege law. 

d) The body of law that the trial court determines in its discretion is most appropriate in the circumstances.