Which of the following polymers may be classified as step growth polymer?

Step growth polymers (or condensation polymers) are prepared by reaction between two functional groups and thereby eliminating small molecules during polymerization. Nylon-6,6 is an example of step growth polymer. Nylon polymerizes by the step-growth polymerization process in which difunctional monomers containing equal parts of amine and carboxylic acid react so that amides are formed at both ends of each monomer. Polyacrylonitrile, Polyisoprene and Polythene polymerize by chain-growth polymerization of acrylonitrile, isoprene (2-methyl-1,3-butadiene) and ethene, respectively.