Section 58(c) of the Transfer of Property Act, 1882 turns an ostensible sale into a mortgage by conditional sale whenever the sale deed and the condition of retransfer on repayment are contained in the same document. Testing each option against this same-document rule, and against what happens once the repayment period lapses, identifies the right answer.
Since the sale and the condition of retransfer sit in one document, the transaction is a mortgage by conditional sale, and B needs a court decree of foreclosure to become absolute owner.
Hence, the correct answer is It is a mortgage by conditional sale; B must seek foreclosure through court.