Which of the following are vinyl chlorides?
$(a)$ $3\text{-chlorocyclohexene}$
$(b)$ $1\text{-chlorocyclohexene}$
$(c)$ $4\text{-chlorobut-1-ene}$
$(d)$ $1\text{-chloroethene}$
$(e)$ $3\text{-chlorobut-1-yne}$
$(f)$ $3\text{-chloro-2-methylpropene}$

• A
  $a, e, f$
• B
  $c, f$
• C
  $b, d$
• D
  $a, f$