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

A saturated carbon chain with a chlorine on alternate carbons is poly(vinyl chloride), PVC. Each repeat unit -CH2-CHCl- comes from chloroethene (vinyl chloride), $\mathrm{CH}{}_2=\mathrm{CHCl}$, whose double bond opens during addition polymerisation. 1,1-Dichloroethene would put two Cl atoms on one carbon.