The following are monosaccharides: (a) glucose B. maltose C. lactose D. sucrose.

A, glucose can't hydrolyze sugar, which belongs to monosaccharide, and A is correct;

B, maltose is disaccharide, which can be hydrolyzed to form two molecules of glucose. B is correct;

C, lactose belongs to animal disaccharide, which can be hydrolyzed to form one molecule of glucose and one molecule of galactose. C is wrong;

D sucrose is an animal disaccharide, which can be hydrolyzed to form one molecule of glucose and one molecule of fructose. D is wrong.

So choose: a.