A short fragment of the polymer chain (two repeat units, end groups shown) is drawn. Which monomer among the structures shown gives this polymer?

Each backbone carbon pair carries one methyl group and one methyl ester group on the same carbon, the repeat unit of poly(methyl methacrylate), PMMA. The monomer is methyl 2-methylpropenoate (methyl methacrylate). Methyl acrylate lacks the alpha-methyl group, vinyl acetate has the ester oxygen on the carbon, and methacrylic acid is an acid, not a methyl ester.