The correct option is (a) washing cotton fabrics
To elaborate: Fungal cellulase is used in detergents which help in washing cotton fabrics. Treatment with cellulase helps to remove the small fibers which are raised from the cotton thread surface which lowers the color brightness, without damaging the major fibers and restores it as new fabric. It also removes soil particles from wash by hydrolyzing associated with fibers. Serine protease is used as thiol protease detergent industry for bleaching the fabrics. Serine protease is used as metalloproteases in detergent industry for softening water. Alcalase is used in liquid preparation with slurries of enzymes in non-ionic surfactant to remove stubborn strains.