Which of the following compounds is a constituent of the polymer

?

The given polymer structure is a Urea-Formaldehyde resin, a cross-linked copolymer synthesized via a condensation polymerization reaction between Urea and Formaldehyde. During the initial stage of the reaction, the nucleophilic nitrogen atoms of urea attack the electrophilic carbonyl carbon of formaldehyde to form an intermediate known as mono=methylol urea. As polymerization progresses, this intermediate undergoes a condensation reaction with neighboring urea molecules, eliminating a molecule of water for every link formed. Because the oxygen atom from the formaldehyde is entirely removed as part of the leaving water molecule, only the stable methylene group remains in the final polymer backbone to bridge the symmetrical units provided by the urea. Therefore, among the choices provided, both Urea and Formaldehyde are the correct constitutional monomers of this polymer.