The repeating unit of an addition polymer is -CH2-CHCl-\text{-CH}_2\text{-CHCl-}-CH2-CHCl-. What is the formula of the monomer used to make this polymer?
CH3CHCl2\text{CH}_3\text{CHCl}_2CH3CHCl2
CH2ClCH2Cl\text{CH}_2\text{ClCH}_2\text{Cl}CH2ClCH2Cl
CH3CH2Cl\text{CH}_3\text{CH}_2\text{Cl}CH3CH2Cl
CH2=CHCl\text{CH}_2\text{=CHCl}CH2=CHCl