Choice "D" is correct. An instrument is payable on demand if it says that it is payable on demand or is silent regarding the time for payment. An instrument is payable at a definite time only if the latest date on which payment can be made can be determined from the face of the instrument. An instrument payable on June 30 or the following June 30 if the holder wishes is payable at a definite time because the latest date on which payment is due can be determined from the face of the instrument (the following June 30). Clauses extending the time for payment to a further definite time stated in the instrument does not destroy the negotiability of the instrument.
Choice "c" is incorrect. The instrument here is not payable on demand. Neither is it payable at a definite time-even if the person's wedding date is set-because the wedding date could change.
Choice "a" is incorrect. The instrument is not payable on demand. Neither is it payable at a definite time because the extension clause does not set a specific due date.
Choice "b" is incorrect. The note is not payable on demand because it purports to be payable one month in the future. Neither is it payable at a definite time. Because the note is undated, it cannot be determined when the one-month period began or, consequently, when it ends.