For each of the following pairs of polymers state whether it is possible to determine whether one polymer is more likely to crystallize than the other and if it is possible, note which one is the more likely to crystallize.

(a) Linear and atactic poly(vinyl chloride); linear and isotactic polypropylene

(b) Linear and syndiotactic polypropylene; crosslinked cis-polyisoprene

(c) Network phenol-formaldehyde; linear and isotactic polystyrene

(d) Block poly(acrylonitrile-isoprene) copolymer; graft poly(chloroprene-isobutylene) copolymer