Which one of the following is made by using step growth polymerization?

Nylon 6,6 is made by using the step growth polymerization. In step growth polymerization, there is bifunctional and multifunctional monomer react to form first dimer and then longer chain polymers. In nylon 6,6 the hexamethylene diamine and adipic acid reacts with each other and formed the dimer first and then polymerise into long chains.