The repeating unit of polyacrylonitrile is

$$\begin{gathered} -{\mathrm{CH}}_2-\mathrm{CH}- \\ \overline{) } \\ CN \end{gathered}$$

$$\begin{gathered} -{\mathrm{CH}}_2-\mathrm{CH}- \\ \overline{) } \\ \mathrm{OH} \end{gathered}$$

$$\begin{gathered} -{\mathrm{CH}}_2-\mathrm{CH}- \\ \overline{) } \\ C{H}_3 \end{gathered}$$

$$\begin{gathered} -{\mathrm{CH}}_2-\mathrm{CH}- \\ \overline{) } \\ C_6{H}_5 \end{gathered}$$