C

Polymerization converts liquid monomer into a denser PMMA network; the larger the proportion of liquid monomer present, the greater the volume contraction that must occur.  Studies show that increasing the monomer (or low-viscosity diluent) content in acrylic/methacrylate mixes raises the final volumetric shrinkage of the cured resin, leading to distortion and warpage of denture bases [Lu et al., 2005, PMID 15482820; Miao et al., 2012, PMID 34062704].