Which one of the following sections of the Transfer of Property Act is concerned with the doctrine of…

Section 56 provides for marshalling by a subsequent purchaser: where the owner of two properties mortgages both to one person and then sells one of them, the buyer may require the mortgage debt to be satisfied out of the property not sold, so far as it will extend. Section 81 has the parallel rule for a subsequent mortgagee. Section 55 deals with the rights and liabilities of buyer and seller, and section 60 with the right of redemption.