Which of the following will meet the requirement for a negotiable instrument to contain an unconditional promise or order to pay? The instrument itself cannot contain any condition to payment, but it may refer to another writing that does. The instrument may refer to another writing that contains rights or obligations related to the promise or order. The amount promised must be certain, but there may be conditions related to how it is paid. The instrument may not contain any condition to payment and may not refer to another writing that governs the payment