D-Glucopyranose is not broken down into two or more carbohydrates upon hydrolysis, so D-glucopyranose is a monosaccharide.
Lactose hydrolysis yields one molecule each of D-galactopyranose and D-glucopyranose, so lactose is a disaccharide.
Amylose hydrolysis yields many molecules of D-glucopyranose, so amylose is a polysaccharide.