A polymer is made by addition polymerisation.
The repeating unit of the polymer is [-CH2-C(CH3)2-]n\left[\text{-CH}_2\text{-C(CH}_3\text{)}_2\text{-}\right]_n[-CH2-C(CH3)2-]n. Which molecule could have been its monomer?
CH2=C(CH3)2\text{CH}_2\text{=C(CH}_3\text{)}_2CH2=C(CH3)2
CH2=CH-CH3\text{CH}_2\text{=CH-CH}_3CH2=CH-CH3
CH3-CH=CH-CH3\text{CH}_3\text{-CH=CH-CH}_3CH3-CH=CH-CH3
CH3-CH(CH3)-CH3\text{CH}_3\text{-CH(CH}_3\text{)-CH}_3CH3-CH(CH3)-CH3