Which one of the following is a chain growth polymer?

Polystyrene is an addition polymer that results when styrene monomers interconnect (polymerization). In the polymerization, the carbon-carbon $\pi$ bond of the vinyl group is broken and a new carbon-carbon $\sigma$ bond is formed, attaching to the carbon of another styrene monomer to the chain.
Related Theory In chain growth, the polymer chain always grows one monomer at a time. In step growth, the polymer chain doubles with each step. As a result, the rate of growth of the polymer chain is very different in these two cases. Chain growth results in a steady increase in chain length with every coupling step.