For each of the following pairs of polymers, plot and label schematic stress-strain curves on the same graph [i.e., make separate plots for parts (a) to (c)].
(a) Polyisoprene having a number-average molecular weight of 100,000 g/mol and 10% of available sites cross-linked; polyisoprene having a number-average molecular weight of 100,000 g/mol and 20% of available sites cross-linked
(b) Syndiotactic polypropylene having a weight-average molecular weight of 100,000 g/mol; atactic polypropylene having a weight-average molecular weight of 75,000 g/mol
(c) Branched polyethylene having a numbers-average molecular weight of 90,000 g/mol; heavily cross-linked polyethylene having a number-average molecular weight of 90,000 g/mol?