An organic compound (A) of molecular formula C3HO on reaction P/I2 gives C3H7I as (B). (B) on reaction with AgNO produces (C) with formula C3H7NO2 . (C) on reaction with nitrous acid gives (D) of molecular formula C3H6N2O3 . (D) on reaction with KOH produces blue colour. Identify A, B. C, D and explain the reaction.