Buna-$N$ synthetic rubber is a copolymer of:

• A
  $CH_2=CH-CH=CH_2$ and $C_6H_5-CH=CH_2$
• B
  $CH_2=CH-CN$ and $CH_2=CH-CH=CH_2$
• C
  $CH_2=CH-CN$ and $CH_2=CH-C(CH_3)=CH_2$
• D
  $CH_2=CH-C(Cl)=CH_2$ and $CH_2=CH-CH=CH_2$