The structure pictured is mannose because the hydroxyl groups at carbons 2, 3, and 4 are situated cis, cis, and trans (respectively) to the  attached to carbon 5.

The mannose pictured is in alpha form because the hydroxyl group at carbon 1 is trans to the  attached to carbon 5.

The chiral carbon farthest away from carbon 1 is designated as "D" if its hydroxyl group is on the right side in the Fischer projection. In other words, this is D-glucose because the hyroxyl group on carbon "x" is oriented to the right.

The structure is D-ribose because it is a five-carbon aldose with the hydroxyl groups on carbons 2, 3, and 4 all on the right in the Fischer projection.

While glucose, galactose, and fructose are all monosaccharides, lactose is a disaccharide comprised of two monosaccharides, glucose and galactose, joined by a -1,4-glycosidic bond.

In nature, L-sugars are indigestible by humans. In the case of L-glucose, even though our bodies can break down polymers of -D-glucose, it cannot digest L-glucose. 

Out of all the sugars listed, lactose is the only one that is not a monosaccharide. Lactose is composed of a glucose and galactose bound together in a glycosidic linkage.

Glucose is also called "blood sugar" because it is the main sugar found in our blood. Sucrose is what we know as "table sugar" because it is commonly found in our kitchens and used in baking etc. Fructose is also known as "fruit sugar" because it occurs in naturally-occurring fruits, giving them their sweetness. Lactose is sometimes called "milk sugar" because it is found in milk.

Review the specific types of monosaccharides and glycosidic bonds that are involved in these disaccharides. Remember that disaccharides are formed upon dehydration synthesis of two monosaccharides.

Maltose is composed of two glucose monomers with an 1-4 linkage.

Cellobiose is composed of two glucose monomers with a 1-4 linkage.

Sucrose is composed of one glucose monomer and one fructose monomer with an 1-2 linkage.

Lactose is composed of one galactose monomer and one glucose monomer with a 1-4 linkage.

Maltose, which is made up of two glucose monomers joined by an alpha-1,4 linkage, is the correct answer. On the other hand, lactose is made up of one glucose monomer and one galactose monomer, and sucrose is made up of one glucose monomer and one fructose monomer. 

Fructose is a monosaccharide; therefore, it is only made up of one type of carbohydrate. Disaccharides are made up of two types of monosaccharides. For example, lactose is made up of galactose and glucose whereas sucrose is made up of glucose and fructose. Polysaccharides are made up of multiple units of monosaccaharides.