What must a creditor file to claim for back rent due before the petition date?

The correct choice is the proof of claim. In the context of bankruptcy proceedings, a creditor must file a proof of claim to assert their right to receive payment for debts owed, including back rent that is due prior to the petition date. This document formally notifies the bankruptcy court and the debtor of the amount owed and the basis for the debt.

Filing a proof of claim is essential, as it allows the creditor to protect their interests and ensures they are considered in the distribution of any assets available to pay off creditors. It must typically be filed within a specific timeframe established by the bankruptcy court, providing the necessary information for the court to recognize the creditor's claim.

The other choices provided do not serve this specific purpose: a plea for credit is not a standard bankruptcy procedure, and an automatic stay application is related to the halting of collection actions once a bankruptcy petition is filed rather than claiming debts owed. A reorganization plan, on the other hand, is a proposal outlining how a debtor intends to restructure their debts and does not apply to the individual claim by a creditor for back rent.