Which repeating unit could be present in the chain formed when polymerising $\mathrm{1,1\text{-}dichloroethene}$?
- A$\mathrm{-CH_2-CH_2-CCl_2-CCl_2-CH_2-CH_2-}$
- B$\mathrm{-CHCl-CHCl-CHCl-CHCl-CHCl-CHCl-}$
- C$\mathrm{-CH_2-CCl_2-CH_2-CH_2-CH_2-CCl_2-}$
- D$\mathrm{-CCl_2-CCl_2-CH_2-CH_2-CH_2-CCl_2-}$