Answer:
The burden of persuasion and the burden of proceeding with the proof will be on the complainant, since the testimony of the defendant raises a rebuttable presumption that perhaps the check was delivered in the mail. The burden of persuasion lies in a party's responsibility of persuading the jury to decide a matter for it. If t
he matter is equally balanced in the jury's view after all the evidence is in, thus the faction with the burden of persuasion will fail. During a trial, the burden of persuasion doesn't shift from party to party.
Since the plaintiff sued the defendant for the debt, the claimant has the duty of reasoning when the time comes for the jury to make a decision. The burden of proceeding with the proof is the burden of producing sufficient proof to generate a question of fact about the matter concerned.
When a plaintiff creates an argument prima facie, he has fulfilled his burden of proceeding with the proof and shifting the burden on the defendant.
Thus, once the plaintiff made a prima facie case about the defendant's debt, the burden of proceeding with the proof transferred to the defendant. The defendant fulfilled the burden by using an assumption.
Federal Rule 301 provides that a presumption imposes the burden of going forward with the evidence to rebut the presumption upon the party against whom it was directed.