A short fragment of the polymer chain (two repeat units, end groups shown) is drawn. Which of the structures shown is the monomer from which this chain is made by addition polymerisation?

The acetate (ester) group is attached through oxygen to the backbone carbon, which is poly(vinyl acetate). The monomer is vinyl acetate, ethenyl ethanoate, $\mathrm{CH}{}_2=\mathrm{CH}-\mathrm{OCOCH}{}_3$. Methyl acrylate is an isomer but would put the carbonyl carbon on the backbone, vinyl alcohol is unstable and ethyl acetate has no C=C.