A compound (A) with molecular formula $ ext{C}_4 ext{H}_5 ext{N}$ on reduction with DIBAL-H followed by hydrolysis, gives a compound (B). Compound (B) gives positive Tollens' test but does not give iodoform test. Compound (B) can also be obtained when ethanal is treated with dilute $ ext{NaOH}$ followed by heating. Identify (A) and (B). Write the reactions of (A) with DIBAL-H followed by hydrolysis.