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B is corrent because one of the requirements for negotiability is that the instrument be payable on demand or at a definite time. An instrument which by its terms is payable only upon an act or event, uncertain as to time of occurrence, is not payable at a definite time. The instrument’s negotiability is affected by basing the time of payment on the maker’s death. This is an event which is uncertain as to time of occurrence and causes the instrument to be nonnegotiable.
A is incorrect because the promise to maintain collateral is not a second promise that destroys negotiability.
C is incorrect because an instrument may be postdated or antedated and this does not affect its negotiability.
D is incorrect because a negotiable instrument may be made payable at a definite time subject to acceleration at the option of the holder.