The monomer of the polymer
is

• Correct answer
  A

  
  
• B

  $\left(\mathrm{CH}_3\right)_2 \mathrm{C}=\mathrm{C}\left(\mathrm{CH}_3\right)_2$
• C

  $\mathrm{CH}_3 \mathrm{CH}=\mathrm{CH} \cdot \mathrm{CH}_3$
• D

  $\mathrm{CH}_3 \mathrm{CH}=\mathrm{CH}_2$

Solution

The monomer of polymer
is
because
shows cationic polymerisation.

Hence, the correct answer is option: 'A'.