The negotiable instruments are passed freely from one party to another almost in the same way as money. To be negotiable, the letter of credit must include (a) a conditional promise to pay on demand or at a definite time (b) an unconditional promise to pay on demand or at an indefinite time (c) an unconditional promise to pay on demand or at a definite time (d) a conditional promise to pay on demand or at an indefinite time