Which one of the following is a promissory note when A signs the instrument?

Under Section 4 of the Negotiable Instruments Act, 1881, a promissory note must contain an unconditional undertaking, signed by the maker, to pay a certain sum of money to or to the order of a certain person, which "I promise to pay B or order Rs.10,000/- on demand" satisfies. "Mr. B, I. Owe. You. Rs.10,000/-" is a mere acknowledgement of debt without a promise to pay, and "I promise to pay B Rs.10,000/- and such other sums which shall be due to him" is not for a certain sum.