On the basis of molecular forces, which of the following pairs represents elastomers only?

Elastomers are rubber–like solids with elastic properties. In these elastomeric polymers, the polymer chains are held together by the weakest intermolecular forces. These weak binding forces permit the polymer to be stretched. A few ‘crosslinks’ are introduced in betweenthe chains, which help the polymer to retract to its original position after the force is released as in vulcanised rubber. Examples are buna-S, buna-N, neoprene, Bromo Isobutylene Isoprene (bromobutyl), Viton (a brand of synthetic rubber and fluoropolymer elastomer commonly used in O-rings and other molded or extruded goods), etc.