Final answer:
Glucose and maltose are reducing sugars because they have free aldehyde groups or can form them under certain conditions, allowing them to act as reducing agents. Starch and cellulose, both polysaccharides, do not fulfill this criterion and are not reducing sugars.
Step-by-step explanation:
Reducing sugars are carbohydrates that can act as reducing agents because they have a free aldehyde group or a free ketone group. Starch and cellulose are both polysaccharides and do not have a free aldehyde group or ketone group available to act as reducing agents. Glucose is a monosaccharide, and it definitely is a reducing sugar as it can exist in an open-chain form with an aldehyde group. Maltose, a disaccharide, is also a reducing sugar because it consists of two glucose molecules joined in such a way that the anomeric carbon of one can open to form an aldehyde group.
Therefore, the reducing sugars from the provided options are glucose and maltose.