Since this fact pattern is designed to test several potential objections to a promissory note at once, it helps to knock each possible objection down in turn.
With every possible technical objection addressed and dismissed, the note stands as fully valid and binding on A.
\[ \boxed{\text{The promissory note is valid; A is liable to pay B.}} \]Another way to work through this fact pattern is to check the note against the basic requirements the law sets for a valid promissory note, rather than against the specific objections raised by the wrong options.
Checking the note against the actual essentials required by law, rather than against invented conditions, confirms its validity.
Hence, the correct answer is The promissory note is valid; A is liable to pay B.